STRSTR(3)

💅 STRSTR(3) — the library-functions-manual girlies are gonna eat this up

okay so bestie. this is a page from the Library Functions Manual about strstr, strcasestr, and strnstr — the "where is my substring" squad. they all live in the Standard C Library (libc, link with -lc). no cap, these are the finders of the string world 🔍✨

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🎀 NAME

strstr, strcasestr, strnstr — locate a substring in a string

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📚 LIBRARY

Standard C Library (libc, -lc)

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✨ SYNOPSIS

like, here's the whole cast, okay 💖

#include <string.h>

char *
strstr(const char *big, const char *little);

char *
strcasestr(const char *big, const char *little);

char *
strnstr(const char *big, const char *little, size_t len);

#include <string.h>
#include <xlocale.h>

char *
strcasestr_l(const char *big, const char *little, locale_t loc);

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🦋 DESCRIPTION

so the way this works:

• strstr() finds the first time the null-terminated string little shows up inside the null-terminated string big. main character search behavior, honestly.
• strcasestr() is literally strstr() but it ignores the case of both strings. so "BAR" and "bar" are the same vibe to it 🙈
• strcasestr_l() does the exact same thing as strcasestr() but takes an explicit locale (locale_t loc) instead of just using whatever the current locale is. very "i brought my own settings" of it.
• strnstr() finds the first occurrence of the null-terminated string little in the string big, but it searches not more than len characters. any characters that show up after a '\0' character are not searched, periodt.

⚠️ important vibe check: strnstr() is a FreeBSD specific API, so it should only be used when portability is not a concern. like, she's iconic but she does NOT travel well 💀 use her only when you don't need your code to run everywhere.

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🫶 RETURN VALUES

okay so the returns, listen up:

• if little is an empty string → big is returned
• if little occurs nowhere in big → NULL is returned
• otherwise → you get a pointer to the first character of the first occurrence of little

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🌸 EXAMPLES

first one sets the pointer ptr to the "Bar Baz" portion of largestring, slay:

const char *largestring = "Foo Bar Baz";
const char *smallstring = "Bar";
char *ptr;

ptr = strstr(largestring, smallstring);

and this next one sets the pointer ptr to NULL, because only the first 4 characters of largestring are searched. yeah. sad but correct 😭

const char *largestring = "Foo Bar Baz";
const char *smallstring = "Bar";
char *ptr;

ptr = strnstr(largestring, smallstring, 4);

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👑 SEE ALSO

go read these too, iykyk:

memchr(3), memmem(3), strchr(3), strcspn(3), strpbrk(3), strrchr(3), strsep(3), strspn(3), strtok(3), wcsstr(3)

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⭐ STANDARDS

strstr() conforms to ISO/IEC 9899:1990 (“ISO C90”). certified classic behavior 🎀

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🌈 HISTORY

strnstr() was introduced by FreeBSD 4.5 and is non-standard. she's a specialty, not a standard-issue icon 💅

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and that's the whole page, bestie 🧚 from the Debian build, dated October 11, 2001 — old but still serving 💜