STRCAT(3) Linux Programmer's Manual STRCAT(3)NAME
strcat, strncat - concatenate two strings
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, over‐
writing 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
As with strcat(), the resulting string in dest is always null-termi‐
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:
strncat(char *dest, const char *src, size_t n)
size_t dest_len = strlen(dest);
for (i = 0 ; i < n && src[i] != '\0' ; i++)
dest[dest_len + i] = src[i];
dest[dest_len + i] = '\0';
The strcat() and strncat() functions return a pointer to the resulting
Multithreading (see pthreads(7))
The strcat() and strncat() functions are thread-safe.
SVr4, 4.3BSD, C89, C99.
Some systems (the BSDs, Solaris, and others) provide the following
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 null
terminator 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 cre‐
ate; if the return value is greater than or equal to size, data loss
occurred. If data loss matters, the caller must either check the argu‐
ments 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.
SEE ALSObcopy(3), memccpy(3), memcpy(3), strcpy(3), string(3), strncpy(3),
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GNU 2014-01-20 STRCAT(3)