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STRCAT(3) Library Functions Manual STRCAT(3)


strcat, strncatconcatenate strings


Standard C Library (libc, -lc)


#include <string.h>

char *
strcat(char * restrict s, const char * restrict append);

char *
strncat(char * restrict s, const char * restrict append, size_t count);


The strcat() and strncat() functions append a copy of the nul-terminated string append to the end of the nul-terminated string s, then add a terminating ‘\0’. The string s must have sufficient space to hold the result.

The strncat() function appends not more than count characters where space for the terminating ‘\0’ should not be included in count.


The strcat() and strncat() functions return the pointer s.


The following appends “abc” to “chararray”:

char *letters = "abcdefghi"; 
(void)strncat(chararray, letters, 3);

The following example shows how to use strncat() safely in conjunction with strncpy(3).

char buf[BUFSIZ]; 
char *input, *suffix; 
(void)strncpy(buf, input, sizeof(buf) - 1); 
buf[sizeof(buf) - 1] = '\0'; 
(void)strncat(buf, suffix, sizeof(buf) - 1 - strlen(buf));

The above will copy as many characters from “input” to “buf” as will fit. It then appends as many characters from suffix as will fit (or none if there is no space). For operations like this, the strlcpy(3) and strlcat(3) functions are a better choice, as shown below.

(void)strlcpy(buf, input, sizeof(buf)); 
(void)strlcat(buf, suffix, sizeof(buf));


The strcat() and strncat() functions conform to ISO/IEC 9899:1999 (“ISO C99”).
August 11, 2002 NetBSD 7.0