std::tmpnam
| Defined in header <cstdio>
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| char* tmpnam( char* filename ); |
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Creates a unique filename that does not name a currently existing file, and stores it in the 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 already be in use, and thus not suitable return values.
std::tmpnam modifies static state and is 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 a null pointer is passed, a pointer to an internal static buffer is returned. |
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 std::tmpnam are difficult to guess, it is possible that a file with that name is created by another process between the moment std::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 (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 <iostream> #include <cstdio> #include <string> int main() { std::string name1 = std::tmpnam(nullptr); std::cout << "temporary file name: " << name1 << '\n'; char name2[L_tmpnam]; if (std::tmpnam(name2)) { std::cout << "temporary file name: " << name2 << '\n'; } }
Possible output:
temporary file name: /tmp/fileDjwifs temporary file name: /tmp/fileEv2bfW
See also
| creates and opens a temporary, auto-removing file (function) | |
| (C++17) |
returns a directory suitable for temporary files (function) |