tmpnam
| Defined in header <stdio.h>
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| char *tmpnam( char *filename ); |
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Creates an unique filename 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.
tmpnam is not reentrant and thus not thread-safe.
Contents |
Parameters
| filename | - | pointer to the character string to be used as a result buffer. If NULL is passed, a pointer to an internal static buffer is returned.
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Return value
filename if filename was not NULL. Otherwise a pointer to an internal static buffer is returned. If no suitable filename can be generated, NULL is returned.
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 std::tmpfile and the POSIX function mkstemp do not have this problem.
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
Code generates a unique filename.
#include <stdlib.h> #include <stdio.h> int main(void) { printf("TMP_MAX = %d\n", TMP_MAX); printf("L_tmpnam = %d\n", L_tmpnam); char buffer[L_tmpnam] = {'\0'}; char * fname = tmpnam(buffer); if (fname == NULL) { fprintf(stderr,"tmpnam() failed in file %s at line # %d\n", __FILE__,__LINE__-3); perror("tmpnam()"); exit(EXIT_FAILURE); } printf("%s\n", fname); printf("%s\n", buffer); exit(EXIT_SUCCESS); }
Output:
TMP_MAX = 238328 L_tmpnam = 20 /tmp/file0JqNEM /tmp/file0JqNEM
See also
| (C11) |
returns a pointer to a temporary file (function) |
| C++ documentation for tmpnam
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