fopen, fopen_s

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Types and objects
Functions
File access
Direct input/output
Unformatted input/output
(until 哋它亢11)(哋它亢11)
(哋它亢95)(哋它亢95)
(哋它亢95)
(哋它亢95)(哋它亢95)
(哋它亢95)
(哋它亢95)
(哋它亢95)
(哋它亢95)
Formatted input
(哋它亢11)(哋它亢11)(哋它亢11)
(哋它亢95)(哋它亢95)(哋它亢95)(哋它亢11)(哋它亢11)(哋它亢11)    
(哋它亢99)(哋它亢99)(哋它亢99)(哋它亢11)(哋它亢11)(哋它亢11)
(哋它亢99)(哋它亢99)(哋它亢99)(哋它亢11)(哋它亢11)(哋它亢11)     
Formatted output
(哋它亢99)(哋它亢11)(哋它亢11)(哋它亢11)(哋它亢11)
(哋它亢95)(哋它亢95)(哋它亢95)(哋它亢11)(哋它亢11)(哋它亢11)(哋它亢11)    
(哋它亢99)(哋它亢11)(哋它亢11)(哋它亢11)(哋它亢11)
(哋它亢95)(哋它亢95)(哋它亢95)(哋它亢11)(哋它亢11)(哋它亢11)(哋它亢11)
File positioning
Error handling
Operations on files
(哋它亢11)
(哋它亢11)
 
Defined in header <stdio.h>
(1)
(until 哋它亢99)
(since 哋它亢99)
errno_t fopen_s( MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 13 HOURS 19 MINUTES 36 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE *restrict *restrict streamptr,

                 const char *restrict filename,

                 const char *restrict mode );
 (2) (since 哋它亢11)
1) Opens a file indicated by filename and returns a pointer to the file stream associated with that file. mode is used to determine the file access mode.
2) Same as (1), except that the pointer to the file stream is written to streamptr and the following errors are detected at runtime and call the currently installed MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 13 HOURS 19 MINUTES 35 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE function:
  • streamptr is a null pointer
  • filename is a null pointer
  • mode is a null pointer
As with all bounds-checked functions, fopen_s only guaranteed to be available if __STDC_LIB_EXT1__ is defined by the implementation and if the user defines __STDC_WANT_LIB_EXT1__ to the integer constant 1 before including MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 13 HOURS 19 MINUTES 34 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE.

Parameters

filename - file name to associate the file stream to
mode - null-terminated character string determining MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 13 HOURS 19 MINUTES 33 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE
streamptr - pointer to a pointer where the function stores the result (an out-parameter)

File access flags

File access
mode string 		Meaning Explanation Action if file
already exists 		Action if file
does not exist
"r" read Open a file for reading read from start failure to open
"w" write Create a file for writing destroy contents create new
"a" append Append to a file write to end create new
"r+" read extended Open a file for read/write read from start error
"w+" write extended Create a file for read/write destroy contents create new
"a+" append extended Open a file for read/write write to end create new
File access mode flag "b" can optionally be specified to open a file in binary mode. This flag has no effect on POSIX systems, but on Windows it disables special handling of '\n' and '\x1A'.
On the append file access modes, data is written to the end of the file regardless of the current position of the file position indicator.
The behavior is undefined if the mode is not one of the strings listed above. Some implementations define additional supported modes (e.g. MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 13 HOURS 19 MINUTES 31 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE).
In update mode ('+'), both input and output may be performed, but output cannot be followed by input without an intervening call to MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 13 HOURS 19 MINUTES 30 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE, MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 13 HOURS 19 MINUTES 29 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE, MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 13 HOURS 19 MINUTES 27 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE or MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 13 HOURS 19 MINUTES 26 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE, and input cannot be followed by output without an intervening call to MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 13 HOURS 19 MINUTES 25 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE, MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 13 HOURS 19 MINUTES 24 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE or MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 13 HOURS 19 MINUTES 22 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE, unless the input operation encountered end of file. In update mode, implementations are permitted to use binary mode even when text mode is specified.
File access mode flag "x" can optionally be appended to "w" or "w+" specifiers. This flag forces the function to fail if the file exists, instead of overwriting it. (哋它亢11)
When using fopen_s or freopen_s, file access permissions for any file created with "w" or "a" prevents other users from accessing it. File access mode flag "u" can optionally be prepended to any specifier that begins with "w" or "a", to enable the default fopen permissions. (哋它亢11)

Return value

1) If successful, returns a pointer to the new file stream. The stream is fully buffered unless filename refers to an interactive device. On error, returns a null pointer. MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 13 HOURS 19 MINUTES 21 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE that MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN 13 HOURS 19 MINUTES 20 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE be set in this case.
2) If successful, returns zero and a pointer to the new file stream is written to *streamptr. On error, returns a non-zero error code and writes the null pointer to *streamptr (unless streamptr is a null pointer itself).

Notes

The format of filename is implementation-defined, and does not necessarily refer to a file (e.g. it may be the console or another device accessible though filesystem API). On platforms that support them, filename may include absolute or relative filesystem path.

Example

Run this code
#include <stdio.h>
#include <stdlib.h>
 
int main(void)
{
    const char* fname = "/tmp/unique_name.txt"; // or tmpnam(NULL);
    int is_ok = MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN  13 HOURS 19 MINUTES 19 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE;
 
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    if (!fp) {
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        return is_ok;
    }
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    int c; // note: int, not char, required to handle EOF
    while ((c = MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN  13 HOURS 19 MINUTES 12 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE(fp)) != MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN  13 HOURS 19 MINUTES 11 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE) // standard C I/O file reading loop
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    if (MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN  13 HOURS 19 MINUTES 09 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE(fp))
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    else if (MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN  13 HOURS 19 MINUTES 06 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE(fp)) {
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        is_ok = MYMEMORY WARNING: YOU USED ALL AVAILABLE FREE TRANSLATIONS FOR TODAY. NEXT AVAILABLE IN  13 HOURS 19 MINUTES 04 SECONDS VISIT HTTPS://MYMEMORY.TRANSLATED.NET/DOC/USAGELIMITS.PHP TO TRANSLATE MORE;
    }
 
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    return is_ok;
}

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Hello, world!
End of file is reached successfully

References

  • 哋它亢17 standard (ISO/IEC 9899:2018):
  • 7.21.5.3 The fopen function (p: 223-224)
  • K.3.5.2.1 The fopen_s function (p: 428-429)
  • 哋它亢11 standard (ISO/IEC 9899:2011):
  • 7.21.5.3 The fopen function (p: 305-306)
  • K.3.5.2.1 The fopen_s function (p: 588-590)
  • 哋它亢99 standard (ISO/IEC 9899:1999):
  • 7.19.5.3 The fopen function (p: 271-272)
  • 哋它亢89/C90 standard (ISO/IEC 9899:1990):
  • 4.9.5.3 The fopen function

See also

 closes a file
(function)
synchronizes an output stream with the actual file
(function)
(哋它亢11)
 open an existing stream with a different name
(function)
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