Predefined Functions for Character Strings

The following functions process character strings. Unless otherwise specified, their prototypes are located in the cstring header.

strlen

strlen( const char* str );

Returns the length of the string str, i.e., the number of characters in the string whose first character is located at the address stored in str. The null character is not counted.

Examples:

cout << strlen("exam"); // 4
    char s[10]="child";
    cout << strlen(s); // 5
    cout << strlen(s + 2); // 3

strcpy

strcpy( char* dest, const char* src );

Copies the characters from the string located at the address src, including the null character, into the string whose first element is at the address dest.

The function returns the address dest.

Examples:

char s[21], t[21] = "child";
    strcpy(s , "exam");
    cout << s; // exam
    strcpy(s , t);
    cout << s; // child
    strcpy(s , t + 2);
    cout << s; // ild
    strcpy(s + 2 , t);
    cout << s; // ilchild

strcat

strcat( char *dest, const char *src );

Appends (concatenates) the characters from the string located at the address src, including the null character, to the string whose first element is at the address dest.

The function returns the address dest.

Examples:

char s[21]="exam", t[21] = "child";
    strcat(s , t);
    cout << s; // examchild
    strcat(s , t + 2);
    cout << s; // examchildild

strchr

strchr( char * str, char ch );

Searches for the character ch in the string whose first character is located at the memory address str.

The function returns the NULL address if the character ch does not appear in the string str, or the address of the first occurrence of ch in str if ch appears.

Examples:

char s[21]="exam";
    char * p = strchr(s , 'x');
    cout << p; // xam

char ch = 'i';
    if(strchr("aeiou" , ch) != NULL)
      cout << "YES";
    else
      cout << "NO";
    // will output YES

strstr

strstr( char * s, char * t );

Searches for the string t in the string whose first character is located at the memory address s.

The function returns the NULL address if the string t does not appear in the string s, or the address of the first occurrence of t in s if t appears.

Examples:

char s[21]="baccalaureate";
    char * p = strstr(s , "cal");
    cout << p; // calaureate

strcmp

strcmp( char * s, char * t );

Lexicographically compares the two character strings:

• if the string s is lexicographically less than t, the function returns a negative value
• if the string s is lexicographically greater than t, the function returns a positive value
• if the two strings are identical, the function returns 0

Examples:

char s[21]="steam", t[21]="primary";
    if(strcmp(s , t) < 0)
      cout << "Yes"
    else
      cout << "No";
    // will output No; the word "steam" is lexicographically after "primary"

strtok

strtok( char *str, const char *sep );

The strtok function extracts from a character string one substring (word) delimited by characters from the sep string. The function is called in two ways:

• the first call has as parameters the string from which extraction is performed and the string of separators
• in subsequent calls, the first parameter is NULL.

The result of strtok is the starting address of the current substring extracted, or NULL if no more substring can be extracted from the given string.

Example:

The sequence below extracts words (separated by characters from the set {' ', ',', '.'}) from a string s and prints them on separate lines. Assume the string s is declared and read.

char sep[]=" .,";
    char * p = strtok(s , sep);
    while(p != NULL)
    {
        cout << p << endl;
        p = strtok(NULL , sep);
    }

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