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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ATTRIBUTES | CONFORMING TO | NOTES | EXAMPLE | SEE ALSO | COLOPHON |
STRCAT(3) Linux Programmer's Manual STRCAT(3)
strcat, strncat - concatenate two strings
#include <string.h>
char *strcat(char *dest, const char *src);
char *strncat(char *dest, const char *src, size_t n);
The strcat() function appends the src string to the dest string,
overwriting the terminating null byte ('\0') at the end of dest, and
then adds a terminating null byte. The strings may not overlap, and
the dest string must have enough space for the result. If dest is
not large enough, program behavior is unpredictable; buffer overruns
are a favorite avenue for attacking secure programs.
The strncat() function is similar, except that
* it will use at most n bytes from src; and
* src does not need to be null-terminated if it contains n or more
bytes.
As with strcat(), the resulting string in dest is always null-
terminated.
If src contains n or more bytes, strncat() writes n+1 bytes to dest
(n from src plus the terminating null byte). Therefore, the size of
dest must be at least strlen(dest)+n+1.
A simple implementation of strncat() might be:
char *
strncat(char *dest, const char *src, size_t n)
{
size_t dest_len = strlen(dest);
size_t i;
for (i = 0 ; i < n && src[i] != '\0' ; i++)
dest[dest_len + i] = src[i];
dest[dest_len + i] = '\0';
return dest;
}
The strcat() and strncat() functions return a pointer to the
resulting string dest.
For an explanation of the terms used in this section, see
attributes(7).
┌────────────────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├────────────────────┼───────────────┼─────────┤
│strcat(), strncat() │ Thread safety │ MT-Safe │
└────────────────────┴───────────────┴─────────┘
POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.
Some systems (the BSDs, Solaris, and others) provide the following
function:
size_t strlcat(char *dest, const char *src, size_t size);
This function appends the null-terminated string src to the string
dest, copying at most size-strlen(dest)-1 from src, and adds a
terminating null byte to the result, unless size is less than
strlen(dest). This function fixes the buffer overrun problem of
strcat(), but the caller must still handle the possibility of data
loss if size is too small. The function returns the length of the
string strlcat() tried to create; if the return value is greater than
or equal to size, data loss occurred. If data loss matters, the
caller must either check the arguments before the call, or test the
function return value. strlcat() is not present in glibc and is not
standardized by POSIX, but is available on Linux via the libbsd
library.
Because strcat() and strncat() must find the null byte that
terminates the string dest using a search that starts at the
beginning of the string, the execution time of these functions scales
according to the length of the string dest. This can be demonstrated
by running the program below. (If the goal is to concatenate many
strings to one target, then manually copying the bytes from each
source string while maintaining a pointer to the end of the target
string will provide better performance.)
Program source
#include <string.h>
#include <time.h>
#include <stdio.h>
int
main(int argc, char *argv[])
{
#define LIM 4000000
int j;
char p[LIM];
time_t base;
base = time(NULL);
p[0] = '\0';
for (j = 0; j < LIM; j++) {
if ((j % 10000) == 0)
printf("%d %ld\n", j, (long) (time(NULL) - base));
strcat(p, "a");
}
}
bcopy(3), memccpy(3), memcpy(3), strcpy(3), string(3), strncpy(3),
wcscat(3), wcsncat(3)
This page is part of release 4.12 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
GNU 2016-07-17 STRCAT(3)
Pages that refer to this page: string(3), wcscat(3), wcsncat(3), feature_test_macros(7), signal-safety(7)