copying
      void *memcpy(void *s1, cont void *s2, size_t n);
      void *memmove(void *s1, const void *s2, size_t n);
      char *strcpy(char *s1, const char *s2);
      char *strncpy(char *s1, const char *s2, size_t n);
      char *strcat(char *s1, const char *s2);
      char *strncat(char *s1, const char *s2, size_t n);
    comparison functions
      int memcmp(const void *s1, const void *s2, size_t n);
      int strcmp(const char *s1, const char *s2);
      int strcoll(const char *s1, const char *s2);
      int strncmp(const char *s1, const char *s2, size_t n);
      int strxfrm(char *s1, const char *s2, size_t n);
    search functions
      void *memchr(const void *s, int c, size_t n);
      char *strchr(const char *s, int c);
      size_t strcspn(const char *s1, const char *s2);
      char *strpbrk(const char *s1, const char *s2);
      char *strrchr(const char *s, int c);
      size_t strspn(const char *s1, const char *s2);
      char *strstr(const char *s1, const char *s2);
      char *strtok(char *s1, const char *s2);
    other functions
      void *memset(void *s, int c, size_t n);
      char *strerror(int errnum);
      size_t strlen(const char *s);