tmpnam, tmpnam_s
Defined in header <stdio.h>
|
||
---|---|---|
|
(1) | |
|
(2) | (since C11) |
1) Creates a unique valid file name (no longer than L_tmpnam
in length) and stores it in character string pointed to by filename
. The function is capable of generating up to TMP_MAX
of unique filenames, but some or all of them may be in use in the filesystem and thus not suitable return values.
2) Same as (1), except that up to TMP_MAX_S
names may be generated, no longer than L_tmpnam_s
in length, and the following errors are detected at runtime and call the currently installed constraint handler function:
filename_s
is a null pointermaxsize
is greater thanRSIZE_MAX
maxsize
is less than the generated file name string
As with all bounds-checked functions, tmpnam_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
.
tmpnam
and tmpnam_s
modify static state (which may be shared between these functions) and are not required to be thread-safe.
Parameters
filename | - | pointer to the character array capable of holding at least L_tmpnam bytes, to be used as a result buffer. If null pointer is passed, a pointer to an internal static buffer is returned.
|
filename_s | - | pointer to the character array capable of holding at least L_tmpnam_s bytes, to be used as a result buffer.
|
maxsize | - | maximum number of characters the function is allowed to write (typically the size of the filename_s array).
|
Return value
1) filename
if filename
was not a null pointer. Otherwise a pointer to an internal static buffer is returned. If no suitable filename can be generated, null pointer is returned.
2) Returns zero and writes the file name to filename_s
on success. On error, returns non-zero and writes the null character to filename_s[0]
(only if filename_s
is not null and maxsize
is not zero and is not greater than RSIZE_MAX
).
Notes
Although the names generated by tmpnam
are difficult to guess, it is possible that a file with that name is created by another process between the moment tmpnam
returns and the moment this program attempts to use the returned name to create a file. The standard function tmpfile
and the POSIX function mkstemp do not have this problem (creating a unique directory using only the standard C library still requires the use of tmpnam
).
POSIX systems additionally define the similarly named function tempnam()
, which offers the choice of a directory (which defaults to the optionally defined macro P_tmpdir)
.
Example
#include <stdio.h>
#include <string.h>
int main(void)
{
char* name1 = tmpnam(NULL);
printf("temporary file name: %s\n", name1);
char name2[L_tmpnam];
if (tmpnam(name2))
printf("temporary file name: %s\n", name2);
}
Possible output:
temporary file name: /tmp/fileRZHMwL
temporary file name: /tmp/file420gSN
References
C11 standard (ISO/IEC 9899:2011):
- 7.21.4.4 The tmpnam function (p: 303-304)
- K.3.5.1.2 The tmpnam_s function (p: 587-588)
C99 standard (ISO/IEC 9899:1999):
- 7.19.4.4 The tmpnam function (p: 269-270)
C89/C90 standard (ISO/IEC 9899:1990):
- 4.9.4.4 The tmpnam function
See also
(C11) |
returns a pointer to a temporary file (function) |
© cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
http://en.cppreference.com/w/c/io/tmpnam