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# std::strtok

From cppreference.com
< cpp‎ | string‎ | byte

Defined in header `<cstring>` |  |
char* strtok( char* str, const char* delim ); |  |

Finds the next token in a null-terminated byte string pointed to by `str`. The separator characters are identified by null-terminated byte string pointed to by `delim`.

This function is designed to be called multiples times to obtain successive tokens from the same string.

- If str != NULL, the call is treated as the first call to `strtok` for this particular string. The function searches for the first character which is not contained in `delim`.

  - If no such character was found, there are no tokens in `str` at all, and the function returns a null pointer.
  - If such character was found, is it the beginning of the token. The function then searches from that point on for the first character that is contained in `delim`.
    - If no such character was found, `str` has only one token, and the future calls to `strtok` will return a null pointer
    - If such character was found, it is replaced by the null character '\0' and the pointer to the following character is stored in a static location for subsequent invocations.
  - The function then returns the pointer to the beginning of the token

- If str == NULL, the call is treated as a subsequent calls to `strtok`: the function continues from where it left in previous invocation. The behavior is the same as if the previously stored pointer is passed as str.

### [edit] Parameters

str | - | pointer to the null-terminated byte string to tokenize
delim | - | pointer to the null-terminated byte string identifying delimiters

### [edit] Return value

Pointer to the beginning of the next token or NULL if there are no more tokens.

### [edit] Notes

This function is destructive: it writes the '\0' characters in the elements of the string `str`. In particular, a string literal cannot be used as the first argument of `strtok`.

Each call to this function modifies a static variable: is not thread safe.

Unlike most other tokenizers, the delimiters in `strtok` can be different for each subsequent token, and can even depend on the contents of the previous tokens.

### [edit] Example

Run this code

    #include <cstring>
    #include <iostream>

    int main()
    {
        char input[100] = "A bird came down the walk";
        char *token = std::strtok(input, " ");
        while (token != NULL) {
            std::cout << token << '\n';
            token = std::strtok(NULL, " ");
        }
    }

Output:

    A
    bird
    came
    down
    the
    walk

### [edit] See also

strpbrk | finds the first location of any character from a set of separators (function) [edit]
strcspn | returns the length of the maximum initial segment that consists of only the characters not found in another byte string (function) [edit]
strspn | returns the length of the maximum initial segment that consists of only the characters found in another byte string (function) [edit]
C documentation for strtok

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