NAME
strcat, strncat - concatenate two strings SYNOPSIS
#include
char *strcat(char *dest, const char *src); char *strncat(char *dest, const char *src, sizet n); DESCRIPTION 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 bytes.
As with strcat(), the resulting string in dest is always null-termi‐ nated. 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, sizet n) { sizet destlen = strlen(dest); sizet i; for (i = 0 ; i < n && src[i] != '\0' ; i++) dest[destlen + i] = src[i]; dest[destlen + i] = '\0'; return dest; } RETURN VALUE The strcat() and strncat() functions return a pointer to the resulting string dest. ATTRIBUTES For an explanation of the terms used in this section, see attributes(7). ┌────────────────────┬───────────────┬─────────┐ │Interface │ Attribute │ Value │ ├────────────────────┼───────────────┼─────────┤
│strcat(), strncat() │ Thread safety │ MT-Safe │ └────────────────────┴───────────────┴─────────┘ CONFORMING TO SVr4, 4.3BSD, C89, C99. NOTES Some systems (the BSDs, Solaris, and others) provide the following function: sizet strlcat(char *dest, const char *src, sizet 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 ALSO bcopy(3), memccpy(3), memcpy(3), strcpy(3), string(3), strncpy(3), wcscat(3), wcsncat(3) COLOPHON
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GNU 2012-07-19 STRCAT(3)