A RetroSearch Logo

Home - News ( United States | United Kingdom | Italy | Germany ) - Football scores

Search Query:

Showing content from https://en.cppreference.com/w/cpp/language/../algorithm/../../cpp/../cpp/../cpp/../c/io/fopen.html below:

fopen, fopen_s - cppreference.com

(1) FILE *fopen( const char *filename, const char *mode ); (until C99) FILE *fopen( const char *restrict filename, const char *restrict mode ); (since C99) errno_t fopen_s( FILE *restrict *restrict streamptr,

                 const char *restrict filename,

                 const char *restrict mode ); (2) (since C11)

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

constraint handler

function:

As with all bounds-checked functions,

fopen_s

is 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

<stdio.h>

.

[edit] Parameters filename - file name to associate the file stream to mode - null-terminated character string determining file access mode streamptr - pointer to a pointer where the function stores the result (an out-parameter) [edit] 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. Windows). In update mode ('+'), both input and output may be performed, but output cannot be followed by input without an intervening call to fflush, fseek, fsetpos or rewind, and input cannot be followed by output without an intervening call to fseek, fsetpos or rewind, 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. (C11) 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. (C11) [edit] 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.

POSIX requires

that

errno

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).

[edit] 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.

[edit] Example 
#include <stdio.h>
#include <stdlib.h>
 
int main(void)
{
    const char* fname = "/tmp/unique_name.txt"; // or tmpnam(NULL);
    int is_ok = EXIT_FAILURE;
 
    FILE* fp = fopen(fname, "w+");
    if (!fp)
    {
        perror("File opening failed");
        return is_ok;
    }
    fputs("Hello, world!\n", fp);
    rewind(fp);
 
    int c; // note: int, not char, required to handle EOF
    while ((c = fgetc(fp)) != EOF) // standard C I/O file reading loop
        putchar(c);
 
    if (ferror(fp))
        puts("I/O error when reading");
    else if (feof(fp))
    {
        puts("End of file is reached successfully");
        is_ok = EXIT_SUCCESS;
    }
 
    fclose(fp);
    remove(fname);
    return is_ok;
}

Possible output:

Hello, world!
End of file is reached successfully
[edit] References
[edit] See also

RetroSearch is an open source project built by @garambo | Open a GitHub Issue

Search and Browse the WWW like it's 1997 | Search results from DuckDuckGo

HTML: 3.2 | Encoding: UTF-8 | Version: 0.7.4