BIO_PRINTF(3ossl)

💖 BIO_PRINTF 💖

ok so this is the BIO_printf(3ossl) page from the OpenSSL fam — it's all about formatted output going to a BIO instead of your boring old stdout. bestie, if you've ever wanted printf but ✨somewhere else✨, this is your moment.

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🌸 NAME 🌸

BIO_printf, BIO_vprintf, BIO_snprintf, BIO_vsnprintf — formatted output to a BIO. that's the whole vibe. four functions, one mission: put your formatted text where you actually want it. 💅

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✨ SYNOPSIS ✨

#include <openssl/bio.h>

int BIO_printf(BIO *bio, const char *format, ...);
int BIO_vprintf(BIO *bio, const char *format, va_list args);

int BIO_snprintf(char *buf, size_t n, const char *format, ...);
int BIO_vsnprintf(char *buf, size_t n, const char *format, va_list args);

like, literally just include the header and you're in. 🫶

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🦋 DESCRIPTION 🦋

okay so let's go one by one, no cap:

• BIO_printf() — it's giving standard C printf(), except the output goes to the BIO you specify, bio, instead of standard output. and yes, all common format specifiers are supported. slay. 🔥
• BIO_vprintf() — this one's the vprintf() of the family (the version found on many platforms). output goes to the specified BIO, bio, not standard output. all common format specifiers supported. the argument list args is a stdarg argument list. iykyk. 💜
• BIO_snprintf() — this one's for the platforms that don't have the common snprintf() function. it's like sprintf() except the size parameter, n, specifies the size of the output buffer. protective queen behavior honestly. 🎀
• BIO_vsnprintf() — the way that BIO_vsnprintf() is to BIO_snprintf() is exactly how BIO_vprintf() is to BIO_printf(). matching set, iconic. ⭐

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👑 RETURN VALUES 👑

all of them return the number of bytes written, or -1 on error. and for BIO_snprintf() and BIO_vsnprintf(), that -1 includes when the output buffer is too small. 😭 so yeah, check your return values, bestie.

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🌈 NOTES 🌈

except when n is 0, both BIO_snprintf() and BIO_vsnprintf() always terminate their output with '\0'. this includes the cases where -1 is returned — like when there's not enough space to output the whole string. so even when it goes wrong, it still null-terminates. main character energy fr fr. 💀

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💜 COPYRIGHT 💜

Copyright 2017-2021 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at <https://www.openssl.org/source/license.html>.

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and that's the page, bestie 🧚 this was OpenSSL 3.5.0, dated 2026-09-25 — drink some water, go format something pretty, and remember: always terminate your strings. 🍓💖