View source for c/io/tmpfile

{{c/title|tmpfile, tmpfile_s}}
{{c/io/navbar}}
{{dcl begin}}
{{dcl header|stdio.h}}
{{dcl|num=1|
FILE* tmpfile( void );
}}
{{dcl|num=2|since=c11|
errno_t tmpfile_s( FILE* restrict* restrict streamptr );
}}
{{dcl end}}

@1@ Creates and opens a temporary file. The file is opened as binary file for update (as if by {{lc|fopen}} with {{c/core|"wb+"}} mode). The filename of the file is guaranteed to be unique within the filesystem. At least {{lc|TMP_MAX}} files may be opened during the lifetime of a program (this limit may be shared with {{lc|tmpnam}} and may be further limited by {{lc|FOPEN_MAX}}).

@2@ Same as {{v|1}}, except that at least {{lc|TMP_MAX_S}} files may be opened (the limit may be shared with {{lc|tmpnam_s}}), and if {{c|streamptr}} is a null pointer, the currently installed [[c/error/set_constraint_handler_s|constraint handler]] function is called.
:{{c/ext1 availability|tmpfile_s}}

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.

===Parameters===
@1@ (none)
@2@ pointer to a pointer that will be updated by this function call

===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 {{c|streamptr}} was a null pointer. In addition, pointer to the associated file stream is stored in {{c|*streamptr}} on success, and a null pointer value is stored in {{c|*streamptr}} on error.

===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 [https://man7.org/linux/man-pages/man2/open.2.html {{tt|open()}}] syscall.

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

===Example===
{{example|code=
#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);
}
|p=true
|output=
TMP_MAX = 238328, FOPEN_MAX = 16
got back from the file: 'Hello'
File name: /tmp/tmpfjptPe5 (deleted)
}}

===References===
{{ref std c23}}
{{ref std|section=7.21.4.3|title=The tmpfile function|p=TBD}}
{{ref std|section=K.3.5.1.1|title=The tmpfile_s function|p=TBD}}
{{ref std end}}
{{ref std c17}}
{{ref std|section=7.21.4.3|title=The tmpfile function|p=222}}
{{ref std|section=K.3.5.1.1|title=The tmpfile_s function|p=427}}
{{ref std end}}
{{ref std c11}}
{{ref std|section=7.21.4.3|title=The tmpfile function|p=303}}
{{ref std|section=K.3.5.1.1|title=The tmpfile_s function|p=586-587}}
{{ref std end}}
{{ref std c99}}
{{ref std|section=7.19.4.3|title=The tmpfile function|p=269}}
{{ref std end}}
{{ref std c89}}
{{ref std|section=4.9.4.3|title=The tmpfile function}}
{{ref std end}}

===See also===
{{dsc begin}}
{{dsc inc|c/io/dsc tmpnam}}
{{dsc see cpp|cpp/io/c/tmpfile}}
{{dsc end}}

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