需求描述

这两天的C语言开发工作中用到了多次字符串格式化拼接，分享一下自己写的一个接口，动态分配内存，减少因缓冲区大小不够导致字符串被截断的烦恼

代码实现

核心代码

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdarg.h>
 
 
int str_append_to_string(char **str, const char *fmt, ...) 
{
    int ret = 0;
    char *ptr = NULL;
    va_list args;
    int limit_size = 0;
    static int init_size = 256;
    static int use_size = 0;
    int size = 0;
    int append_ok = 0;
 
    if (fmt == NULL || strlen(fmt) <= 0)
    {
        printf("[%s:%d] param error\n", __FUNCTION__, __LINE__);
        return -1;
    }
 
    ptr = *str;
    if (ptr == NULL)
    {
        ptr = (char *)malloc(init_size * sizeof(char));
        if (ptr == NULL)
        {
            printf("[%s:%d] malloc failed\n", __FUNCTION__, __LINE__);
            return -1;
        }
        
        init_size = 256;
        use_size = 0;
        memset(ptr, 0, (init_size * sizeof(char)));
    }
 
    do
    {
        limit_size = init_size - use_size - 1;
 
        va_start(args, fmt);
        size = vsnprintf((ptr + use_size), limit_size, fmt, args);
        va_end(args);
 
        if (size > 0 && size <= limit_size)
        {
            use_size += size;
            append_ok = 1;
            continue;
        }
 
        // need more memory
        init_size += init_size >> 2;
        char *ptr_backup = ptr; // 备份ptr指针
        ptr = (char *)realloc(ptr, init_size * sizeof(char)); // realloc失败的话，ptr之前malloc的内存是不会被释放的
        if (ptr == NULL)
        {
            printf("[%s:%d] realloc failed\n", __FUNCTION__, __LINE__);
            ptr = ptr_backup; // 还原ptr指针
            ret = -1;
            break;
        }
    } while(!append_ok);
 
    *str = ptr;
 
    return ret;
}

调用代码

int main(int argc, char*argv[])
{
    int ret = -1;
    char *string = NULL;
    ret = str_append_to_string(&string, "letters/%s/id_card/%d/name/%s", "ABC", 123, "Bob");
    if (ret == 0)
    {
        printf("string:%s\n", string);
    }
    
    if (string != NULL)
    {
        free(string);
        string = NULL;
    }
 
    return 0;
}