Extract string between two specific strings in C

问题

How do you extract strings between two specified strings? For Example: <title>Extract this</title>. Is there a simple way to get it using strtok() or anything simpler?

EDIT: The two specified strings are <title> and </title> and the string extracted is Extract this.

回答1:

Search for the first sub string using strstr().
If found, save the array index of the sub string
From there, search for the next sub string.
If found, everything between [ [start of sub string 1] + [length of sub string 1] ] and [start of sub string 2] is the string you are interested in.
Extract the string using strncpy() or memcpy().

回答2:

This is an example of how you can do it, it's not checking the input string integrity

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

char *extract(const char *const string, const char *const left, const char *const right)
{
    char  *head;
    char  *tail;
    size_t length;
    char  *result;

    if ((string == NULL) || (left == NULL) || (right == NULL))
        return NULL;
    length = strlen(left);
    head   = strstr(string, left);
    if (head == NULL)
        return NULL;
    head += length;
    tail  = strstr(head, right);
    if (tail == NULL)
        return tail;
    length = tail - head;
    result = malloc(1 + length);
    if (result == NULL)
        return NULL;
    result[length] = '\0';

    memcpy(result, head, length);
    return result;
}

int main(void)
{
    char  string[] = "<title>The Title</title>";
    char *value;

    value = extract(string, "<title>", "</title>");
    if (value != NULL)
        printf("%s\n", value);
    free(value);

    return 0;
}

回答3:

The answer by Mr. @Lundin is nice one. However, just to add a bit more generic approach, (without depending on the <tag> value itself), you can also do like,

Locate the first instance of < [tag opening angle bracket] using strchr()
find the first first instance of > [tag closing angle bracket] using strchr().
save the indexes and the difference of two indexes, copy the string to a temporary array. will treat as the tag value.
Locate the last instance of < [tag opening angle bracket] using strrchr()
find the last instance of > [tag closing angle bracket] using strrchr().
Again, save the indexes and the difference of two indexes, copy the string to another temporary array. Compare with previously stored tag value, if equals, do a memcpy() / strdup() from acualarray[first_last_index] (closing starting tag) upto acualarray[last_first_index] (starting of closing tag.)

来源：https://stackoverflow.com/questions/30302294/extract-string-between-two-specific-strings-in-c

标签

string

strtok