std::tmpnam(3)

🌸 NAME 🌸

std::tmpnam — std::tmpnam. Welcome to the std::tmpnam(3) page from the C++ Standard Libary, bestie 💖. This is the function that makes a filename vibe into existence.

📜 Synopsis

Defined in header <cstdio>:

char* tmpnam( char* filename );

It 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 😭.

Also, std::tmpnam modifies static state and is not required to be thread-safe. Not thread-safe, periodt. 💅

🎀 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 a null pointer.
• Otherwise, a pointer to an internal static buffer is returned.
• If no suitable filename can be generated, a null pointer 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. That's the race-condition jump scare 🙈.

Bestie, this is the important bit: 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). No cap.

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). Extra choices, iconic. ✨

💻 Example

// Run this code

#include <cstdio>
#include <iostream>
#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

• tmpfile — creates and opens a temporary, auto-removing file (function).
• temp_directory_path — returns a directory suitable for temporary files (C++17) (function).
• C documentation for tmpnam.

💖 That's the whole page, bestie! Source: http://cppreference.com · version/date: 2024.06.10 · manual tag: std::tmpnam(3). Bye! 🎀✨