c-json.c

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

/**
 * @author kangear@163.com
 * @data 2014-12-17
 * @param dst name num
 * @return boolean
 * such as:[{"name1":1, "name2":2}]
 */
#define JSON_BUFFER_SIZE 1024
int add_json(char* dst, const char* name, const int num) {
    const char* const head = "[{";
    const char* const end  = "}]";
    char *p_dst = NULL;
    int first_time = 0;

    if (name == NULL)
        goto err;
    
    /* redirect */
    p_dst = dst + strlen(dst);

    /* is first time in here */
    if (strlen(dst) < 4) {
        first_time = 1;
    }    

    /* add "[{" start or remove '}]' */
    if (first_time == 1) {
        strncpy(p_dst, head, strlen(head));
        p_dst += strlen(head);
    } else {
        p_dst -= strlen(end);
        sprintf(p_dst, "%s", ",");
        p_dst += 1;
    }

    /* insert new string */
    p_dst += sprintf(p_dst, "\"%s\":%d", name, num);

    /* add '}]' at end */
    sprintf(p_dst, "%s", end);

    return EXIT_SUCCESS;

err:
    return EXIT_FAILURE;
}

int main() {
    //char buf[256] = "[{\"name1\":1, \"name2\":2}]";
    char buf[256] = {0};
    add_json(buf, "Black", 60);
    add_json(buf, "Color", 70);
    add_json(buf, "name3", 4);
    printf("%s\n", buf);
}

/**
 * [{"Black:":100,"Color:":70}]
 */