C中的数组和strpbrk

Question

If my array is :

char* String_Buffer = "Hi my name is <&1> and i have <&2> years old."
char* pos = strpbrk(String_buffer, "<");

Now pos is :

" <&1> and i have <&2> years old. "

But i need "Hi my name is". How can do this?

Answer 1

First, make sure that the string you are working with is in modifiable memory ¹ :

char String_Buffer[] = "Hi my name is <&1> and i have <&2> years old."

then, cut your string at the position where you found < :

char* pos = strpbrk(String_buffer, "<");
if(pos!=NULL)
{
    /* changing the '<' you found to the null character you are actually
     * cutting the string in that place */
    *pos=0;
}

Printing String_Buffer will now output Hi my name is . If you don't want the final space, just move pos backward of one element (being careful not to go before the beginning of String_Buffer ).

---

1. In your code you declared a char pointer and made it point to a string literal, which is non-modifiable (that's why you normally write const char * str = "asdasads"; ; in this case, instead, we are initializing a local char array, which we can change as much as we want.

Answer 2

If you track start separately, you can "cut out" a section of the buffer:

char *start = String_Buffer;
char *end = strpbrk(String_Buffer, "<");

if (end) {
    /* found it, allocate enough space for it and NUL */
    char *match = malloc(end - start + 1);

    /* copy and NUL terminate */
    strncpy(match, start, end - start);
    match[end - start] = '\0';

    printf("Previous tokens: %s\n", match);
    free(match);
} else {
    /* no match */
}

To walk the buffer printing each token, you'll simply hoist this into a loop:

char *start = String_Buffer, *end, *match;

while (start) {
    end = strpbrk(start, "<");
    if (!end) {
        printf("Last tokens: %s\n", start);
        break;
    } else if (end - start) {
        match = malloc(end - start + 1);

        /* copy and NUL terminate */
        strncpy(match, start, end - start);
        match[end - start] = '\0';

        printf("Tokens: %s\n", match);
        free(match);

        end++; /* walk past < */
    }

    /* Walk to > */
    start = strpbrk(end, ">");
    if (start) {
        match = malloc(start - end + 1); /* start > end */
        strncpy(match, end, start - end);
        match[start - end] = '\0';

        printf("Bracketed expression: %s\n", match);
        free(match);
        start++; /* walk past > */
    }
}