Difference between <string.h> and <strings.h>
strings.h comes from the BSD branch in the unix evolution. Its content has been standardized by POSIX, but most of it is marked as legacy and can be easily replaced with other functions:
int bcmp(const void *, const void *, size_t); /* LEGACY, see memcmp */void bcopy(const void *, void *, size_t); /* LEGACY, see memcpy, memmove */void bzero(void *, size_t); /* LEGACY, see memset */int ffs(int);char *index(const char *, int); /* LEGACY, see strchr */char *rindex(const char *, int); /* LEGACY, see strrchr */int strcasecmp(const char *, const char *);int strncasecmp(const char *, const char *, size_t);
Typically <strings.h> just adds some useful but non-standard additional string functions to the standard header <string.h>. For maximum portability you should only use <string.h> but if you need the functions in <strings.h> more than you need portability then you can use <strings.h> instead of <string.h>.