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strncat(3) Library Functions Manual strncat(3) NAME strncat, strncmp, strncpy - Perform operations on string LIBRARY Standard C Library (libc.so, libc.a) SYNOPSIS #include <string.h> char *strncat( char *s1, const char *s2, size_t n); int strncmp( const char *s1, const char *s2, size_t n); char *strncpy( char *s1, const char *s2, size_t n); STANDARDS Interfaces documented on this reference page conform to industry stan- dards as follows: strncat(), strncmp(), strncpy(): XPG4, XPG4-UNIX Refer to the standards(5) reference page for more information about in- dustry standards and associated tags. PARAMETERS Points to a location containing the first string or array. Points to a location containing the second array. Specifies the number of bytes. In strncat(), n specifies the maximum number of bytes to append; in strncmp(), n specifies the maximum number of bytes to compare; and in strncpy(), n specifies the number of bytes to copy. DESCRIPTION The strncat() function appends no more than n bytes from the array pointed to by the s2 parameter to the end of the array pointed to by the s1 parameter. The initial byte of the array pointed to by s2 over- writes the null byte at the end of a string pointed to by s1. It then appends a null byte to the result, and returns s1. When operating on overlapping objects, the behavior of this function is unreliable. The strncmp() function compares the string or array pointed to by the s1 parameter to the array pointed to by the s2 parameter. The sign of a nonzero value returned by strcmp() is determined by the sign of the difference between the values of the first pair of bytes (both inter- preted as unsigned char) that differ in the two compared objects. The strncmp() functions compares bytes until it has compared n bytes or un- til it reaches a terminating null byte. The strncmp() function compares objects based on the machine collating order. It does not use the locale-dependent sorting order. Use the strcoll() or wcscoll() functions for locale-dependent sorting. The strncpy() function copies no more than n bytes from the array pointed to by the s2 parameter to the array pointed to by the s1 para- meter. Bytes following a null byte are not copied. When operating on overlapping locations, the behavior of this function is unreliable. When the location pointed to by the s2 parameter is an array that is shorter than n bytes, null bytes are appended to the s1 value until n bytes in all are written. RETURN VALUES Upon successful completion, the strncat() and strncpy() functions re- turn a pointer to the resulting string or array. [Digital] Otherwise, these functions return a null pointer. Upon successful completion, the strncmp() function returns an integer whose value is greater than, equal to, or less than 0 (zero), according to whether the value of the s1 object is greater than, equal to, or less than the value of the s2 object. [Digital] When a successful com- parison cannot be made, strncmp() returns a value of 0 (zero). RELATED INFORMATION Functions: string(3), strcasecmp(3), strcat(3), strcmp(3), strcoll(3), strcpy(3), wcscoll(3), wcsncat(3), wcsncmp(3), wcsncpy(3) Standards: standards(5) delim off strncat(3)