从 strtok 中反转标记会导致空字符串

Question

I am attempting to reverse the words/tokens returned from strtok, I am iterating over each token in reverse order and assigning each ith value to a buffer called new . I can print each ith value/char of the token pointer p but for some reason I am having trouble assigning the chars p is pointing to the buffer new . What am I missing or doing wrong here?

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

int main(void) {
    char str[] = "This is an example!";
    char *new = malloc(strlen(str));
    char *p = strtok(str, " ");
    size_t j = 0;
    while (1) {
        for (size_t i=strlen(p)-1; i>-1; i--) {
            new[j++] = p[i];
        }
        p = strtok(NULL, " ");
        if (!p)
            break;
        new[j++] = ' ';
    }
    printf("%s\n", new);
    return 0;
}

stdout:

Intended/expected output:

sihT si na !elpmaxe

Answer 1

• Terminating null-character will be added to the buffer new because the initial value of the loop is strlen(p) . It should be strlen(p)-1 .
• The type of i should be ssize_t (signed type) instead of size_t (unsigned type) to have i>-1 work well.
• One more byte should be allocated for new and terminating null-character should be added at the end of string.

Try this:

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

int main(void) {
    char str[] = "This is an example!";
    char *new = malloc(strlen(str)+1); /* allocate one more byte */
    char *p = strtok(str, " ");
    size_t j = 0;
    while (1) {
        for (ssize_t i=strlen(p)-1; i>-1; i--) { /* fix loop */
            new[j++] = p[i];
        }
        p = strtok(NULL, " ");
        if (!p)
            break;
        new[j++] = ' ';
    }
    new[j] = '\0'; /* add terminating null-character */
    printf("%s\n", new);
    return 0;
}