The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition
Copyright © 2001-2004 The IEEE and The Open Group, All Rights reserved.
A newer edition of this document exists here


lsearch, lfind - linear search and update


[XSI] [Option Start] #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 *)); [Option End]


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. The key argument points to the entry to be sought in the table. The base argument points to the first element in the table. The width argument is the size of an element in bytes. 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. 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.

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.


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


No errors are defined.

The following sections are informative.


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.

#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 "This is a test.".

#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);


The comparison function need not compare every byte, so arbitrary data may be contained in the elements in addition to the values being compared.

Undefined results can occur if there is not enough room in the table to add a new item.






hcreate(), tsearch(), the Base Definitions volume of IEEE Std 1003.1-2001, <search.h>


First released in Issue 1. Derived from Issue 1 of the SVID.

Issue 6

The DESCRIPTION is updated to avoid use of the term "must" for application requirements.

End of informative text.

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