CSE 40872 Lecture 007

Strings (C)

Array of char terminated by '\0' (NULL).

char  s[MAX_STRLEN];
char *sptr;

sptr = malloc(sizeof(char) * MAX_STRLEN);

Functions (Length)

strlen(const char *s):

Returns length of string NOT including '\0'.

size_t strlen(const char *s) {
    size_t i;

    for (i = 0; s[i] != 0; i++) ;

    return (i);
}

Functions (Comparison)

strcmp(const char * s1, const char *s2):

Returns negative if s1 < s2, 0 if s1 == s2, positive if s1 > s2

strcasecmp:

Same as strcmp but ignores case.

if (strcmp(s1, s2) == 0)
    printf("%s is the same as %s\n", s1, s2);

Functions (Search)

strchr(const char *s, int c):

Returns a pointer to the first occurrence of character c in s, NULL if not found.

strstr(const char *s1, const char *s2):

Returns a pointer to the first occurrence of s2 in s1, NULL if not found.

strrchr, strrstr:

Same as above but searches from the end of the string.

Functions (Search)

char *strrchr(const char *s, int c) {
    char *sp;

    for (sp = s[strlen(s) - 1]; sp != s; sp--)
        if (*sp == c)
            return (sp);

    return (NULL);
}

Functions (Copy)

strcpy(char *dst, const char *src):

Copies string src into string dst.

char *strcpy(char *dst, const char *src) {
    char *dp, *sp;

    dp = dst;
    sp = src;
    while (*sp != 0)
        *dp++ = *sp++;

    return (dst);
}

Functions (Concatenate)

strcat(char *dst, const char *src):

Concatenates string src at the end of dst.

char s[MAX_STRLEN];

strcpy(s, "Hello, ");
strcat(s, "World!");

Functions (Tokenize)

strtok(char *s, const char *delim):

Parses a string into tokens delimited by characters in delim. Tokens will not contain delimiters.

char *s = "words separated by spaces.";
char *d = " ";
char *sp;

sp = strtok(s, d);
while (sp) {
    puts(sp);
    sp = strtok(NULL, d);
}

Tips

#include <string.h> // C
#include <cstring>  // C++

• Some functions include a n variant where you can specify the length of strings; this can be more efficient, and usually safer.

• Check man pages for more information:

  $ man string
  $ man strlen