Fopen s c как использовать

man pages section 3: Basic Library Functions

The fopen() function opens the file whose pathname is the string pointed to by filename, and associates a stream with it.

The argument mode points to a string beginning with one of the following sequences:

Open file for reading

Truncate to zero length or create file for writing

Append; open or create file for writing at end-of-file

Open file for update (reading and writing)

Truncate to zero length or create file for update

Append; open or create file for update, writing at end-of-file

The character b has no effect, but is allowed for ISO C standard conformance (see standards(7)). Opening a file with read mode (r as the first character in the mode argument) fails if the file does not exist or cannot be read.

Opening a file with exclusive mode (x somewhere after the initial w or a in the mode argument) fails if the file already exists or cannot be created.

Opening a file with append mode (a as the first character in the mode argument) causes all subsequent writes to the file to be forced to the then current end-of-file, regardless of intervening calls to fseek(3C). If two separate processes open the same file for append, each process may write freely to the file without fear of destroying output being written by the other. The output from the two processes will be intermixed in the file in the order in which it is written.

When a file is opened with update mode (+ as the second or third character in the mode argument), both input and output may be performed on the associated stream. However, output must not be directly followed by input without an intervening call to fflush(3C) or to a file positioning function (fseek(3C), fsetpos(3C), or rewind(3C)), and input must not be directly followed by output without an intervening call to a file positioning function, unless the input operation encounters end-of-file.

When opened, a stream is fully buffered if and only if it can be determined not to refer to an interactive device. The error and end-of-file indicators for the stream are cleared.

If mode begins with w or a and the file did not previously exist, upon successful completion, fopen() function will mark for update the st_atime, st_ctime and st_mtime fields of the file and the st_ctime and st_mtime fields of the parent directory.

If mode begins with w and the file did previously exist, upon successful completion, fopen() will mark for update the st_ctime and st_mtime fields of the file. The fopen() function will allocate a file descriptor as open(2) does.

The largest value that can be represented correctly in an object of type off_t will be established as the offset maximum in the open file description.

Additional mode characters are supported in this implementation. These additional characters must appear after r, w, or a.

Specifying e in the mode argument indicates the file is being opened with the O_CLOEXEC flag. This sets the FD_CLOEXEC for the underlying file descriptor. For more information, see the open(2) man page.

Specifying f in the mode argument indicates the file is being opened with the O_CLOFORK flag. This sets the FD_CLOFORK for the underlying file descriptor. For more information, see the open(2) man page.

Specifying x in the mode argument indicates the file is being opened in exclusive mode; the file is opened with the O_EXCL flag. For more information, see the open(2) man page.

The fopen_s() function is part of the bounds checking interfaces specified in the C11 standard, Annex K. It is similar to the fopen() function, except for a different return type and an additional parameter, providing extra safety checks in the form of explicit runtime-constraints as defined in the C11 standard. The fopen_s() function provides a new mode character, u which may precede any of the previously defined modes starting with the character w or a. See INCITS/ISO/IEC 9899:2011.

Implementation specific details for fopen_s() include the following:

Files opened for writing are opened with exclusive, (or non-shared), access. The file permission for the file will prevent other system users from accessing the file, that is S_IRUSR | S_IWUSR flags if the file is being created and the first character of the mode string is not u. For more information, see the chmod(2) man page. If the file is being created and first character of the mode string is u, the file shall have the system default file access permissions.

A runtime-constraint violation will be generated if either streamptr, filename, or mode is a null pointer.

Return Values

Upon successful completion, fopen() returns a pointer to the object controlling the stream. Otherwise, a null pointer is returned and errno is set to indicate the error.

The fopen() function may fail and not set errno if there are no free stdio streams.

If the fopen_s() function succeeds in opening a file, it returns zero. Otherwise, a non-zero value is returned if fopen_s() failed to open the file or if a runtime-constraint violation was encountered.

Errors

The fopen() and fopen_s() functions will fail if:

Search permission is denied on a component of the path prefix, or the file exists and the permissions specified by mode are denied, or the file does not exist and write permission is denied for the parent directory of the file to be created.

A signal was caught during the execution of fopen().

The named file is a directory and mode requires write access.

Too many symbolic links were encountered in resolving filename.

There are <OPEN_MAX> file descriptors currently open in the calling process.

The length of the filename exceeds PATH_MAX or a pathname component is longer than NAME_MAX.

The maximum allowable number of files is currently open in the system.

A component of filename does not name an existing file or filename is an empty string.

The directory or file system that would contain the new file cannot be expanded, the file does not exist, and it was to be created.

A component of the path prefix is not a directory.

The named file is a character special or block special file, and the device associated with this special file does not exist.

The current value of the file position cannot be represented correctly in an object of type fpos_t.

The named file resides on a read-only file system and mode requires write access.

The fopen() function may fail if:

The value of the mode argument is not valid.

<FOPEN_MAX> streams are currently open in the calling process.

<STREAM_MAX> streams are currently open in the calling process.

Pathname resolution of a symbolic link produced an intermediate result whose length exceeds <PATH_MAX>.

Insufficient storage space is available.

The file is a pure procedure (shared text) file that is being executed and mode requires write access.

The fopen_s() function will fail if:

Null pointer is passed.

Usage

The fopen() function has a transitional interface for 64-bit file offsets. For more information, see the lf64(7) man page.

Русские Блоги

Использование функций fopen, fopen_s, fclose, _fcloseall

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Использование функции fopen

После определения FILE * fp, fopen используется: fp = fopen (имя файла, "w"). Для fopen_s мы должны определить другую переменную errno_t err, затем err = fopen_s (& fp, filename, "w"), Обратите внимание, что первый параметр — это указатель на FILE *, который является двойным указателем , Если возвращается значение, для fopen указатель файла (назначенный fp) возвращается, если файл успешно открыт, и возвращается NULL, если он не открывается, для fopen_s файл успешно возвращается 0 в случае сбоя и ненулевое значение в случае сбоя.

В программировании часто встречаются такие предупреждения: предупреждение C4996: «fopen»: эта функция или переменная может быть небезопасной. Попробуйте вместо этого использовать fopen_s. Чтобы отключить устаревание, используйте_CRT_SECURE_NO_WARNINGS. Подробнее см. В интерактивной справке. fopen_s имеет больше обнаружения переполнения, чем fopen (вопрос: где используется обнаружение переполнения, нет ничего похожего на gets_s . ), это более безопасно. (Существует также сравнение между get и get_s и сравнение между strcpy и strcpy_s в будущих статьях. Их общие точки используются для некоторого неожиданного поведения, которое будет подробно объяснено позже)

Closes a stream (fclose) or closes all open streams (_fcloseall).

int fclose( FILE *stream );

int _fcloseall( void );

Function Required Header Compatibility

fclose
<stdio.h>
ANSI, Win 95, Win NT

_fcloseall
<stdio.h>
ANSI, Win 95, Win NT

For additional compatibility information, see Compatibility in the Introduction.

LIBC.LIB
Single thread static library, retail version

LIBCMT.LIB
Multithread static library, retail version

MSVCRT.LIB
Import library for MSVCRT.DLL, retail version

fclose returns 0 if the stream is successfully closed. _fcloseall returns the total number of streams closed . Both functions return EOF to indicate an error.

Pointer to FILE structure

The fclose function closes stream. _fcloseall closes all open streams except stdin, stdout, stderr (and, in MS-DOS®, _stdaux and _stdprn). It also closes and deletes any temporary files created by tmpfile . In both functions, all buffers associated with the stream are flushed prior to closing (примечание: все буферы, связанные с этими потоками, сбрасываются до того, как эти потоки закрываются, поэтому данные не теряются из-за закрытия). System-allocated buffers are released when the stream is closed. Buffers assigned by the user with setbuf and setvbuf are not automatically released.（ СПРОСИТЕ: Каковы функции setbuf и setvbuf? )

_s стратегия использования функции класса

Сначала познакомьтесь с использованием функций gets_s и getws_s. gets_s, _getws_s
https://msdn.microsoft.com/en-us/library/5b5x9wc7.aspx

Gets a line from the stdin stream. These versions of gets, _getws have security enhancements (Повышенная безопасность), как описано вSecurity Features in the CRT.

char *gets_s(
char *buffer,
size_t sizeInCharacters
);
wchar_t *_getws_s(
wchar_t *buffer,
size_t sizeInCharacters
);
template <size_t size>
char *gets_s(
char (&buffer)[size]
); // C++ only
template <size_t size>
wchar_t *_getws_s(
wchar_t (&buffer)[size]
); // C++ only

Storage location for input string.

The size of the buffer.

Returns buffer if successful. A NULL pointer indicates an error or end-of-file condition. Use ferror or feof to determine which one has occurred.

The gets_s function reads a line from the standard input stream stdin and stores it in buffer. The line consists of all characters up to and including the first newline character (‘\n’). gets_s then replaces the newline character with a null character (‘\0’) before returning the line. In contrast, the fgets_s function retains the newline character.

If the first character read is the end-of-file character, a null character is stored at the beginning of buffer and NULL is returned.

_getws is a wide-character version of gets_s; its argument and return value are wide-character strings.

If buffer is NULL or sizeInCharacters is less than or equal to zero, or if the buffer is too small to contain the input line and null terminator, these functions invoke an invalid parameter handler, as described in Parameter Validation. If execution is allowed to continue, these functions return NULL and set errno to ERANGE.

In C++, using these functions is simplified by template overloads; the overloads can infer buffer length automatically (eliminating the need to specify a size argument) and they can automatically replace older, non-secure functions with their newer, secure counterparts. For more information, see Secure Template Overloads.

Кстати, scanf и scanf_s, gets и gets_s (примечание: первая s в gets_s здесь — это строка, которая является строкой, а вторая — безопасна), а здесь fopen_s и fopen, причина с _s Безопасность функций не означает, что об ошибке не сообщается, когда пользовательский ввод превышает длину буфера, но верно обратное. При обнаружении недостаточного буфера будет сообщено об ошибке.

The secure functions do not prevent or correct security errors скорее (но), они отлавливают ошибки, когда они происходят. Они выполняют дополнительные проверки для условий ошибки, и в случае ошибки, они вызывают обработчик ошибок (см. Parameter Validation ).

В отличие от scanf, который получает символы в массив символов, если количество символов, введенных пользователем, превышает длину буфера, scanf может «молчать» ( Примечание: в некоторых компиляторах такая ситуация существует ), Этот метод может не создавать никаких исключений в течение определенного периода времени, но операция не принадлежит его собственному пространству памяти, которое само по себе является уязвимостью, так называемой «уязвимостью переполнения буфера», часто используемой некоторыми хакерами. Подумайте, соответствуют ли эти неправильно обработанные байты ключевым данным или адресу входа функции （ Примечание. В этом случае хакер может использовать уязвимость переполнения буфера, чтобы изменить этот адрес входа на адрес входа программы-троянца, написанной им самим. Ты трагедия! Чисто по слухам, я сам не пробовал! ! )

》》》 Некоторые учащиеся могут быть озадачены способом получения формы ошибки или предупреждения, когда gets_s получает данные, которые превышают длину буфера. На самом деле, я хочу заставить его работать следующим образом.

Во-первых, Когда пользователь вводит длину данных (обратите внимание: что именно нужно выяснить) Когда длина буфера не превышена, все символы перед новой строкой принимаются нормально.

(Примечание: если вы не обращаете внимания, здесь есть еще одна ловушка, конечно, предпосылка заключается в том, что когда вы используете gets_s, ввод содержит как китайский, так и английский и другие западные символы. Написать сообщение О разнице между получением однобайтовых символов и широких символов Войти. (W_char всегда должен использоваться для утилит).

2. Когда длина данных, вводимых пользователем, превышает длину буфера, принимается «значение второго параметра минус один» символов, а последний символ буфера устанавливается в качестве ограничителя. ( СПРОСИТЕ: Как выглядит терминатор в широких символах? Все ли два нуля? ）。

Для нашего второго желания реализация по умолчанию в стандартной библиотеке обычно будет напоминанием об ошибке, но для действительно практического применения пользователи не будут позволять своему программному обеспечению постоянно сообщать об ошибках. В настоящее время мы не будем обсуждать, сколько пользователей будет использовать подчиненное управление. Станция получает программное обеспечение для ввода. Это на самом деле достижимо.

Большинство функций CRT (C runtime) с повышенной безопасностью и многие из ранее существующих функций проверяют свои параметры, включая проверку указателей на NULL, проверку попадания целых чисел в допустимый диапазон или проверку значений перечисления. допустимы. Когда найден неверный параметр, выполняется обработчик недопустимого параметра.
примечание: обратите внимание, что некоторые примеры параметров аутентификации упоминаются в это время, перевод выглядит следующим образом:
Во-первых, является ли указатель пустым.
Во-вторых, попадет ли целое число в допустимый диапазон.
В-третьих, проверьте, допустим ли тип перечисления.
И если найден недопустимый параметр, будет выполнен соответствующий механизм обработки недопустимых параметров. ? ? ? Существует ли механизм обработки для каждого типа исключения параметра?

Invalid Parameter Handler Routine
———————————————————————————
Поведение среды выполнения C при обнаружении недопустимого параметра заключается в вызове назначенного в данный момент недопустимого обработчика параметров. По умолчанию (примечание: это должно относиться к среде выполнения, а не к отладке) неверный параметр вызывает отчет о сбое Watson, который вызывает приложение аварийно завершает работу и спрашивает пользователя, хотят ли они загрузить аварийный дамп в Microsoft для анализа. In Debug mode, an invalid parameter also results in a failed assertion Как показано на рисунке ниже, это окно предупреждения, когда пользовательский ввод, полученный функцией gets_s, превышает длину буфера.

This behavior can be changed by using the function _set_invalid_parameter_handler to set the invalid parameter handler to your own function (Примечание: вы можете установить недопустимый механизм обработки параметров для своей собственной определенной функции через функцию set_invalid_parameter_handler) does not terminate the application управление возвращается функции, получившей недопустимые параметры, и эти функции обычно прекращают выполнение, возвращают код ошибки (примечание: , Имея дело с соответствующей проблемой, я могу вернуть соответствующий код ошибки для неправильного ввода. СПРОСИТЕ: Как использовать возвращаемое и ошибочное значение функции при программировании? ? ? ? ), and set errno to an error code. In many cases, the errno value and the return value are both EINVAL, indicating an invalid parameter. In some cases, a more specific error code is returned , such as EBADF for a bad file pointer passed in as a parameter. For more information on errno, see errno, _doserrno, _sys_errlist, and _sys_nerr.
==========

Fopen s c как использовать

Opens a file. These versions of fopen , _wfopen have security enhancements, as described in Security features in the CRT.

pFile
A pointer to the file pointer that receives the pointer to the opened file.

filename
The name of the file to open.

mode
Type of access permitted.

Zero if successful; an error code on failure. For more information about these error codes, see errno , _doserrno , _sys_errlist , and _sys_nerr .

pFile	filename	mode	Return Value	Contents of pFile
NULL	any	any	EINVAL	unchanged
any	NULL	any	EINVAL	unchanged
any	any	NULL	EINVAL	unchanged

The fopen_s and _wfopen_s functions can’t open a file for sharing. If you need to share the file, use _fsopen or _wfsopen with the appropriate sharing mode constant—for example, use _SH_DENYNO for read/write sharing.

The fopen_s function opens the file specified by filename . _wfopen_s is a wide-character version of fopen_s and the arguments to _wfopen_s are wide-character strings. _wfopen_s and fopen_s behave identically, otherwise.

fopen_s accepts paths that are valid on the file system at the point of execution; UNC paths and paths that involve mapped network drives are accepted by fopen_s as long as the system that’s executing the code has access to the share or mapped network drive at the time of execution. When you construct paths for fopen_s , don’t make assumptions about the availability of drives, paths, or network shares in the execution environment. You can use either forward slashes (/) or backslashes (\) as the directory separators in a path.

These functions validate their parameters. If pFile , filename , or mode is a null pointer, these functions generate an invalid parameter exception, as described in Parameter validation.

Always check the return value to see if the function succeeded before you do any further operations on the file. If an error occurs, the error code is returned, and the global variable errno is set. For more information, see errno , _doserrno , _sys_errlist , and _sys_nerr .

By default, this function’s global state is scoped to the application. To change it, see Global state in the CRT.

fopen_s supports Unicode file streams. To open a new or existing Unicode file, pass a ccs flag that specifies the desired encoding to fopen_s , for example:

fopen_s(&fp, «newfile.txt», «w+, ccs=UNICODE»);

Allowed values of the ccs flag are UNICODE , UTF-8 , and UTF-16LE . If no value is specified for ccs , fopen_s uses ANSI encoding.

If the file already exists and is opened for reading or appending, the byte order mark (BOM), if present in the file, determines the encoding. The BOM encoding takes precedence over the encoding that’s specified by the ccs flag. The ccs encoding is only used when no BOM is present or if the file is a new file.

[!NOTE] BOM-detection only applies to files that are opened in Unicode mode; that is, by passing the ccs flag.

The following table summarizes the modes for various ccs flag values that are given to fopen_s and for BOMs in the file.

Encodings used based on ccs flag and BOM

ccs flag	No BOM (or new file)	BOM: UTF-8	BOM: UTF-16
UNICODE	UTF-8	UTF-8	UTF-16LE
UTF-8	UTF-8	UTF-8	UTF-16LE
UTF-16LE	UTF-16LE	UTF-8	UTF-16LE

Files that are opened for writing in Unicode mode have a BOM written to them automatically.

If mode is «a, ccs=UNICODE» , «a, ccs=UTF-8» , or «a, ccs=UTF-16LE» , fopen_s first tries to open the file with both read access and write access. If successful, the function reads the BOM to determine the encoding for the file; if unsuccessful, the function uses the default encoding for the file. In either case, fopen_s then reopens the file with write-only access. (This behavior applies to a mode only, not a+ .)

The character string mode specifies the kind of access that’s requested for the file, as follows.

mode	Access
«r»	Opens for reading. If the file doesn’t exist or can’t be found, the fopen_s call fails.
«w»	Opens an empty file for writing. If the given file exists, its contents are destroyed.
«a»	Opens for writing at the end of the file (appending) without removing the end-of-file (EOF) marker before new data is written to the file. Creates the file if it doesn’t exist.
«r+»	Opens for both reading and writing. The file must exist.
«w+»	Opens an empty file for both reading and writing. If the file exists, its contents are destroyed.
«a+»	Opens for reading and appending. The appending operation includes the removal of the EOF marker before new data is written to the file. The EOF marker isn’t restored after writing is completed. Creates the file if it doesn’t exist.

When a file is opened by using the «a» or «a+» access type, all write operations occur at the end of the file. The file pointer can be repositioned by using fseek or rewind , but it’s always moved back to the end of the file before any write operation is carried out so that existing data can’t be overwritten.

The «a» mode doesn’t remove the EOF marker before appending to the file. After appending has occurred, the MS-DOS TYPE command only shows data up to the original EOF marker and not any data that’s appended to the file. The «a+» mode does remove the EOF marker before appending to the file. After appending, the MS-DOS TYPE command shows all data in the file. The «a+» mode is required for appending to a stream file that is terminated with the CTRL +Z EOF marker.

When the «r+» , «w+» , or «a+» access type is specified, both reading and writing are allowed. (The file is said to be open for «update».) However, when you switch from reading to writing, the input operation must come across an EOF marker. If there’s no EOF marker, you must use an intervening call to a file-positioning function. The file-positioning functions are fsetpos , fseek , and rewind . When you switch from writing to reading, you must use an intervening call to either fflush or to a file-positioning function.

Starting in C11, you can append «x» to «w» or «w+» to cause the function fail if the file exists, instead of overwriting it.

In addition to the previous values, the following characters can be included in mode to specify the translation mode for newline characters:

mode modifier	Translation mode
t	Open in text (translated) mode. Carriage return-line feed (CR-LF) combinations are translated into single line feeds (LF) on input and LF characters are translated to CR-LF combinations on output. CTRL+Z is interpreted as an end-of-file character on input.
b	Open in binary (untranslated) mode; translations involving carriage-return and line feed characters are suppressed.

In text (translated) mode, CTRL +Z is interpreted as an end-of-file character on input. For files opened for reading/writing with «a+» , fopen_s checks for a CTRL +Z at the end of the file and removes it, if possible. It’s removed because using fseek and ftell to move within a file that ends with a CTRL +Z, may cause fseek to behave improperly near the end of the file.

Also, in text mode, carriage return/line feed (CRLF) combinations are translated into single line feed (LF) characters on input, and LF characters are translated to CRLF combinations on output. When a Unicode stream-I/O function operates in text mode (the default), the source or destination stream is assumed to be a sequence of multibyte characters. The Unicode stream-input functions convert multibyte characters to wide characters (as if by a call to the mbtowc function). For the same reason, the Unicode stream-output functions convert wide characters to multibyte characters (as if by a call to the wctomb function).

If t or b isn’t given in mode , the default translation mode is defined by the global variable _fmode . If t or b is prefixed to the argument, the function fails and returns NULL .

For more information about using text and binary modes in Unicode and multibyte stream-I/O, see Text and binary mode file I/O and Unicode stream I/O in text and binary modes.

mode modifier	Behavior
c	Enable the commit flag for the associated filename so that the contents of the file buffer are written directly to disk if either fflush or _flushall is called.
n	Reset the commit flag for the associated filename to «no-commit.» This flag is the default. It also overrides the global commit flag if you link your program with COMMODE.OBJ . The global commit flag default is «no-commit» unless you explicitly link your program with COMMODE.OBJ (see Link options).
N	Specifies that the file isn’t inherited by child processes.
S	Specifies that caching is optimized for, but not restricted to, sequential access from disk.
R	Specifies that caching is optimized for, but not restricted to, random access from disk.
T	Specifies a file that isn’t written to disk unless memory pressure requires it.
D	Specifies a temporary file that is deleted when the last file pointer to it is closed.
ccs=UNICODE	Specifies UNICODE as the encoded character set to use for this file. Leave unspecified if you want ANSI encoding.
ccs=UTF-8	Specifies UTF-8 as the encoded character set to use for this file. Leave unspecified if you want ANSI encoding.
ccs=UTF-16LE	Specifies UTF-16LE as the encoded character set to use for this file. Leave unspecified if you want ANSI encoding.

Valid characters for the mode string used in fopen_s and _fdopen correspond to oflag arguments used in _open and _sopen , as follows.

Characters in mode string	Equivalent oflag value for _open / _sopen
a	`_O_WRONLY
a+	`_O_RDWR
R	_O_RDONLY
r+	_O_RDWR
w	_O_WRONLY (usually `_O_WRONLY
w+	_O_RDWR (usually **`_O_RDWR
b	_O_BINARY
t	_O_TEXT (translated)
c	None
n	None
D	_O_TEMPORARY
R	_O_RANDOM
S	_O_SEQUENTIAL
T	_O_SHORTLIVED
ccs=UNICODE	_O_WTEXT
ccs=UTF-8	_O_UTF8
ccs=UTF-16LE	_O_UTF16

The c , n , R , S , t , T , and D mode options are Microsoft extensions for fopen_s and _wfopen_s and shouldn’t be used when you want ANSI portability.

If you’re using rb mode, memory mapped Win32 files might also be an option if you don’t need to port your code, you expect to read much of the file, or you don’t care about network performance.

Regarding T and D :

T avoids writing the file to disk as long as memory pressure doesn’t require it. For more information, see FILE_ATTRIBUTE_TEMPORARY in File attribute constants, and also this blog post It’s only temporary.
D specifies a regular file that is written to disk. The difference is that it’s automatically deleted when it’s closed. You can combine TD to get both semantics.

For more information on standards conformance and naming conventions in the C runtime library, see Compatibility.

What is fopen_s in C?

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The fopen_s function in C is used to securely open files in different modes such as reading and writing. It is secure as it performs robust security checks on the arguments passed to it. For example, it would return an error if the pointer passed to it was NULL . Similarly, it requires the file access mode to be specified in its arguments to set the appropriate permission based on user type.

The fopen_s function is only available since the C11 standard. Otherwise, we can not use the function. So make sure that you have C11 enabled on your system!

How to go from fopen to fopen_s

Visual Studio is complaining about fopen. I can’t find the proper syntax for changing it. I have:

What is the rest of the first parameter?

1 Answer 1

fopen_s is a "secure" variant of fopen with a few extra options for the mode string and a different method for returning the stream pointer and the error code. It was invented by Microsoft and made its way into the C Standard: it is documented in annex K.3.5.2.2 of the most recent draft of the C11 Standard. Of course it is fully documented in the Microsoft online help. You do not seem to understand the concept of passing a pointer to an output variable in C. In your example, you should pass the address of filepoint as the first argument:

Here is a complete example:

Microsoft’s support for C99 is clunky and incomplete. Visual Studio produces warnings for valid code, forcing the use of standard but optional extensions but in this particular case does not seem to support strerrorlen_s . Refer to Missing C11 strerrorlen_s function under MSVC 2017 for more information.

To make matters worse, the Microsoft implementation of many of their secure functions have different semantics from the standard one documented in Annex K, which caused other systems to reject these functions and refuse to implement them. It is therefore recommended to avoid them for portability’s sake.

In order to use standard functions such as fopen() with Visual Studio, you can add these 3 lines at the beginning of your source files, before the first #include directive: