A RetroSearch Logo

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

Search Query:

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

tmpfile, tmpfile_s - cppreference.com

(1) errno_t tmpfile_s( FILE* restrict* restrict streamptr ); (2) (since C11) 1)

Creates and opens a temporary file. The file is opened as binary file for update (as if by

fopen

with

"wb+"

mode). The filename of the file is guaranteed to be unique within the filesystem. At least

TMP_MAX

files may be opened during the lifetime of a program (this limit may be shared with

tmpnam

and may be further limited by

FOPEN_MAX

).

2)

Same as

(1)

, except that at least

TMP_MAX_S

files may be opened (the limit may be shared with

tmpnam_s

), and if

streamptr

is a null pointer, the currently installed

constraint handler

function is called.

As with all bounds-checked functions, tmpfile_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>.

The temporary file created by this function is closed and deleted when the program exits normally. Whether it's deleted on abnormal termination is implementation-defined.

[edit] Parameters

1) (none)

2) pointer to a pointer that will be updated by this function call

[edit] Return value

1) Pointer to the file stream associated with the file or null pointer if an error has occurred.

2) Zero if the file was created and open successfully, non-zero if the file was not created or open or if streamptr was a null pointer. In addition, pointer to the associated file stream is stored in *streamptr on success, and a null pointer value is stored in *streamptr on error.

[edit] Notes

On some implementations (e.g. older Linux), this function actually creates, opens, and immediately deletes the file from the file system: as long as an open file descriptor to a deleted file is held by a program, the file exists, but since it was deleted, its name does not appear in any directory, so that no other process can open it. Once the file descriptor is closed, or once the program terminates (normally or abnormally), the space occupied by the file is reclaimed by the filesystem. Newer Linux (since 3.11 or later, depending on filesystem) creates such invisible temporary files in one step, via special flag in the open() syscall.

On some implementations (e.g. Windows), elevated privileges are required as the function may create the temporary file in a system directory.

[edit] Example 
#define _POSIX_C_SOURCE 200112L
#include <stdio.h>
#include <unistd.h>
 
int main(void)
{
    printf("TMP_MAX = %d, FOPEN_MAX = %d\n", TMP_MAX, FOPEN_MAX);
    FILE* tmpf = tmpfile();
    fputs("Hello, world", tmpf);
    rewind(tmpf);
    char buf[6];
    fgets(buf, sizeof buf, tmpf);
    printf("got back from the file: '%s'\n", buf);
 
    // Linux-specific method to display the tmpfile name
    char fname[FILENAME_MAX], link[FILENAME_MAX] = {0};
    sprintf(fname, "/proc/self/fd/%d", fileno(tmpf));
    if (readlink(fname, link, sizeof link - 1) > 0)
        printf("File name: %s\n", link);
}

Possible output:

TMP_MAX = 238328, FOPEN_MAX = 16
got back from the file: 'Hello'
File name: /tmp/tmpfjptPe5 (deleted)
[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