sprintf(3)

💖 sprintf(3) — string print formatted 💖

okay bestie, sit down, hydrate, and let me tell you about sprintf and vsprintf — two functions from the Library Functions Manual that are giving iconic but slightly feral energy. ✨ They live in the standard C library, ngl.

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🌈 LIBRARY 🌈

Standard C library (libc, -lc) 🫶

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📜 SYNOPSIS 📜

#include <stdio.h>

int sprintf(char *restrict str,
            const char *restrict format, ...);
int vsprintf(char *restrict str,
             const char *restrict format, va_list ap);

🎀 Feature Test Macro Requirements for glibc (see feature_test_macros(7)): 🎀

snprintf(), vsnprintf():

_XOPEN_SOURCE >= 500 || _ISOC99_SOURCE
    || /* glibc <= 2.19: */ _BSD_SOURCE

(yes, the macro list really does say snprintf() and vsnprintf() — I'm just the messenger, bestie 💅)

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🌸 DESCRIPTION 🌸

So these two? They're literally equivalent to snprintf(3) and vsnprintf(3)… except there's no check for buffer overrun performed. None. Zero. Not a vibe check in sight. 😭 (peep BUGS below, it's important, iykyk).

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👑 ATTRIBUTES 👑

For an explanation of the terms used in this section, see attributes(7).

• sprintf(), vsprintf() — Thread safety: MT-Safe locale

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⭐ STANDARDS ⭐

C11, POSIX.1-2008. queen behavior, fr fr 💅

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🦋 HISTORY 🦋

C89, POSIX.1-2001. she's been around, she's seen things 🌸

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💀 BUGS 💀

See printf(3).

🙈 sprintf(), vsprintf()

Because sprintf() and vsprintf() assume an arbitrarily long string, callers must be careful not to overflow the actual space — and honestly? this is often impossible to assure. 🫠

Also note that the length of the strings produced is locale-dependent and difficult to predict. so like. unpredictable AND dangerous. not the duo we wanted. 😭

Use snprintf() and vsnprintf() instead (or asprintf(3) and vasprintf(3)). periodt. protect your buffers, protect your peace. 🫶

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🌈 SEE ALSO 🌈

• asprintf(3)
• snprintf(3)

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mwah 💖 that's the whole page, bestie — brought to you by Linux man-pages 6.20, dated 2025-12-07. go forth and not overflow your buffers ✨🎀🦋