split char string with multi-character delimiter in C

问题

I want to split a char *string based on multiple-character delimiter. I know that strtok() is used to split a string but it works with single character delimiter.

I want to split char *string based on a substring such as "abc" or any other sub-string. How that can be achieved?

回答1:

Finding the point at which the desired sequence occurs is pretty easy: strstr supports that:

char str[] = "this is abc a big abc input string abc to split up";
char *pos = strstr(str, "abc");

So, at that point, pos points to the first location of abc in the larger string. Here's where things get a little ugly. strtok has a nasty design where it 1) modifies the original string, and 2) stores a pointer to the "current" location in the string internally.

If we didn't mind doing roughly the same, we could do something like this:

char *multi_tok(char *input, char *delimiter) {
    static char *string;
    if (input != NULL)
        string = input;

    if (string == NULL)
        return string;

    char *end = strstr(string, delimiter);
    if (end == NULL) {
        char *temp = string;
        string = NULL;
        return temp;
    }

    char *temp = string;

    *end = '\0';
    string = end + strlen(delimiter);
    return temp;
}

This does work. For example:

int main() {
    char input [] = "this is abc a big abc input string abc to split up";

    char *token = multi_tok(input, "abc");

    while (token != NULL) {
        printf("%s\n", token);
        token = multi_tok(NULL, "abc");
    }
}

produces roughly the expected output:

this is
 a big
 input string
 to split up

Nonetheless, it's clumsy, difficult to make thread-safe (you have to make its internal string variable thread-local) and generally just a crappy design. Using (for one example) an interface something like strtok_r, we can fix at least the thread-safety issue:

typedef char *multi_tok_t;

char *multi_tok(char *input, multi_tok_t *string, char *delimiter) {
    if (input != NULL)
        *string = input;

    if (*string == NULL)
        return *string;

    char *end = strstr(*string, delimiter);
    if (end == NULL) {
        char *temp = *string;
        *string = NULL;
        return temp;
    }

    char *temp = *string;

    *end = '\0';
    *string = end + strlen(delimiter);
    return temp;
}

multi_tok_t init() { return NULL; }

int main() {
    multi_tok_t s=init();

    char input [] = "this is abc a big abc input string abc to split up";

    char *token = multi_tok(input, &s, "abc");

    while (token != NULL) {
        printf("%s\n", token);
        token = multi_tok(NULL, &s, "abc");
    }
}

I guess I'll leave it at that for now though--to get a really clean interface, we really want to reinvent something like coroutines, and that's probably a bit much to post here.

回答2:

You can easlity write your own parser using strstr() to achieve the same. The basic algorithm may look like this

use strstr() to find the first occurrence of the whole delimiter string
mark the index
copy from starting till the marked index, that will be your expected token.
to parse the input for subsequent entries, adjust the strating of the initial string to advance by token length + length of the delimiter string.

回答3:

EDIT : Considered suggestions from Alan and Sourav and written a basic code for the same .

#include <stdio.h>

#include <string.h>

int main (void)
{
  char str[] = "This is abc test abc string";

  char* in = str;
  char *delim = "abc";
  char *token;

  do {

    token = strstr(in,delim);

    if (token) 
      *token = '\0';

    printf("%s\n",in);

    in = token+strlen(delim);

  }while(token!=NULL);


  return 0;
}

来源：https://stackoverflow.com/questions/29788983/split-char-string-with-multi-character-delimiter-in-c

标签

string

parsing

tokenize

delimiter