从 (void *) 类型取消引用结构 [英] dereferencing structure from (void *) type

问题描述

我正在尝试使用 void 指针传递数据，然后将其转换为 (pData *) 类型.我究竟做错了什么?gcc 给了我

i'm trying to pass data with void pointer and then cast it to (pData *) type. What am i doing wrong? gcc gives me

gcc test.c 错误:在非结构体或联合体中请求成员文件名"

gcc test.c error: request for member ‘filename’ in something not a structure or union

typedef struct data {
        char *filename;
        int a;
} pData;

void mod_struct(void *data) {
        printf("%s\n",(pData *)data->filename); //error on this line
}

void main() {
        pData *data;
        data = (pData *) malloc(sizeof(pData));
        data->filename = (char *)malloc(100);
        strcpy(data->filename,"testing testing");
        data->a=1;
        mod_struct((void *)&data);
}

推荐答案

应该

printf("%s\n", ((pData *) data)->filename);

-> 运算符的优先级高于类型转换运算符.

-> operator has higher precedence than typecast operator.

除此之外，您对 mod_struct 的调用应如下所示

In addition to that your call to mod_struct should look as follows

mod_struct((void *) data);

你所拥有的 & 完全没有意义.当 data 已经是你需要的指针时，你为什么还要取 data 的地址?

That & you have there makes absolutely no sense. Why are you taking the address of data when data is already a pointer to what you need?

这篇关于从 (void *) 类型取消引用结构的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！