[C语言]一个带有可变长度字符串参数的函数在接收长字符串时报错

问题描述

问 题

目标函数，是接受一连串的字符串，可能非常的长，然后把每个字符转化成对应的16进制（字符串格式）
但是如下会报错。但假如我缩短param的字符长度为比如JJJJJJJJJJ，就不会报错了。
由于认为char *character为可变长度且用了malloc不理解为何会过长。求教，非常感谢！

char *convert_to_16(char *characters, int n){

    // int c_length = strlen(characters);
    char sub_buffer[3];
    char code[3];
    char buf[3];
    char *buffer = (char*)malloc(sizeof(characters) * 2);
    for(int i=0; i < n; i++){
        strncpy(code, characters+i, 1);
        code[1+i]=0;
        sprintf(sub_buffer, "%x", *code);
        sprintf(buf, "%s", sub_buffer);
        strncat(buffer, buf, 2);
    } 
    return buffer;
}

int main(){
    char param[] = "JjjjjdddddddddJJJJJJJJJJJJJJJJJdddjjj";
    printf("%s\n", param);
    int length = strlen(param);
    printf("%s\n", convert_to_16(param, length));
}

问题已经解决，去掉code[1+i]就无问题了。但是原理和内存方面的控制貌似会有问题，若有见解欢迎赐教，谢谢！

解决方案

char *convert_to_16(char *characters, int n){

    // int c_length = strlen(characters);
    char sub_buffer[3];
    char code[3];//改为2
    char buf[3];
    char *buffer = (char*)malloc(sizeof(characters) * 2);//长度错误， 改为2n+1
    //增加下面一行，malloc并不会将分配空间初始化为0
    buffer[0]='\0';
    for(int i=0; i < n; i++){
        strncpy(code, characters+i, 1);
        code[1+i]=0;//此处strlen(code)应为1，改为code[1]='\0'
        //下面两个重复可以省略一个
        sprintf(sub_buffer, "%x", *code);
        sprintf(buf, "%s", sub_buffer);
        strncat(buffer, buf, 2);
    }
    return buffer;
}

int main(){
    char param[] = "JjjjjdddddddddJJJJJJJJJJJJJJJJJdddjjj";
    printf("%s\n", param);
    int length = strlen(param);
    printf("%s\n", convert_to_16(param, length));
}

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