LSEARCH(3POSIX)

💖 LSEARCH(3POSIX) — bestie edition 💖

okay so we're in the POSIX Programmer's Manual today, and this page is LSEARCH(3POSIX). quick vibe check before we dive in, because it matters:

⚠️ This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

like, it's giving "the spec says this, your kernel might say otherwise" 😭 always check your local manpage bestie, i'm so serious.

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✨ NAME ✨

lsearch, lfind — linear search and update. yes ma'am, two functions, one icon behavior, we love a duo 💅

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🎀 SYNOPSIS 🎀

#include <search.h>

void *lsearch(const void *key, void *base, size_t *nelp, size_t width,
    int (*compar)(const void *, const void *));
void *lfind(const void *key, const void *base, size_t *nelp,
    size_t width, int (*compar)(const void *, const void *));

look at that signature. clean. immaculate. no notes. 🫶

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🌸 DESCRIPTION 🌸

so here's the tea, bestie ☕

The lsearch() function shall linearly search the table and return a pointer into the table for the matching entry. If the entry does not occur, it shall be added at the end of the table. yes, it just adds it. it's helpful like that 💖

let's break down the arguments because they're a whole friend group:

• The key argument points to the entry to be sought in the table. that's your target, your main character 🔍
• The base argument points to the first element in the table. the origin story.
• The width argument is the size of an element in bytes. know your sizes, fr fr.
• The nelp argument points to an integer containing the current number of elements in the table. The integer to which nelp points shall be incremented if the entry is added to the table. so it keeps count for you, king behavior 👑
• The compar argument points to a comparison function which the application shall supply (for example, strcmp()). It is called with two arguments that point to the elements being compared. The application shall ensure that the function returns 0 if the elements are equal, and non-zero otherwise. yes, zero means equal, non-zero means nope — do not get this backwards or everything falls apart 😭

and now, the plot twist 🌈

The lfind() function shall be equivalent to lsearch(), except that if the entry is not found, it is not added to the table. Instead, a null pointer is returned.

so like... lsearch() is the extrovert who invites everyone to the party, and lfind() is the one who's just looking, thank you very much 🙈 same energy, different boundaries.

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⭐ RETURN VALUE ⭐

If the searched for entry is found, both lsearch() and lfind() shall return a pointer to it. slay.

Otherwise, lfind() shall return a null pointer and lsearch() shall return a pointer to the newly added element.

Both functions shall return a null pointer in case of error. 💀

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🦋 ERRORS 🦋

No errors are defined.

The following sections are informative.

(translation: the spec is not gonna yell at you here. the next sections are just bonus lore, not rules.)

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💅 EXAMPLES 💅

🍓 Storing Strings in a Table

This fragment reads in less than or equal to TABSIZE strings of length less than or equal to ELSIZE and stores them in a table, eliminating duplicates. no dupes allowed in this household 🚫✨

#include <stdio.h>
#include <string.h>
#include <search.h>

#define TABSIZE 50
#define ELSIZE 120

...
    char line[ELSIZE], tab[TABSIZE][ELSIZE];
    size_t nel = 0;
    ...
    while (fgets(line, ELSIZE, stdin) != NULL && nel < TABSIZE)
        (void) lsearch(line, tab, &nel,
            ELSIZE, (int (*)(const void *, const void *)) strcmp);
...

🧚 Finding a Matching Entry

The following example finds any line that reads "Thisisatest.".

#include <search.h>
#include <string.h>
...
char line[ELSIZE], tab[TABSIZE][ELSIZE];
size_t nel = 0;
char *findline;
void *entry;

findline = "This is a test.\n";

entry = lfind(findline, tab, &nel, ELSIZE, (
    int (*)(const void *, const void *)) strcmp);

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🌈 APPLICATION USAGE 🌈

The comparison function need not compare every byte, so arbitrary data may be contained in the elements in addition to the values being compared. so like, your structs can have ✨extra✨ fields that compar just ignores, it's fine, it's valid, it's chic.

⚠️ Undefined results can occur if there is not enough room in the table to add a new item. bestie. please make sure your table has room. undefined behavior is not the moment. 😭

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💜 RATIONALE 💜

None.

(iconic of them honestly. nothing to explain. it just works.)

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⭐ FUTURE DIRECTIONS ⭐

None.

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🔥 SEE ALSO 🔥

• hcreate(), tdelete()

The Base Definitions volume of POSIX.1‐2017, <search.h>

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👑 COPYRIGHT 👑

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

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and that's the whole page bestie, we ate and left no crumbs 🫶 this edition came to you straight from IEEE/The Open Group, 2017 — go forth and linearly search, ily, bye 💖🌸✨