问题：内存对齐、sizeof计算的字节数不对

最新推荐文章于 2022-09-06 23:19:31 发布

原创最新推荐文章于 2022-09-06 23:19:31 发布 · 807 阅读

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#c语言 #sizeof #struct

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本文通过一个C语言示例介绍了内存对齐的概念及其在结构体中的应用。通过对比不同结构体的大小，展示了如何通过编译指令来控制内存对齐，进而优化程序的空间效率。

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1. 脑补内存对齐：

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2. 实验一下：

编译如下的c文件：使用命令gcc main.c

#include <sys/types.h>

#pragma pack(1)
typedef struct _CmdRfidReset {
    //unsigned char a;
    unsigned short int b;
    unsigned char c;
    unsigned char d;
    unsigned char e;
    unsigned char f;
    unsigned char g;
    unsigned char reserved[8];
    unsigned short int crc;
} CmdRfidReset;
typedef CmdRfidReset tSCmdRfidReset;


int main(){

    struct _CmdRfidResetUpload{
        unsigned char a;             //this is different to tSCmdRfidReset
        unsigned short int b;
        unsigned char c;
        unsigned char d;
        //unsigned char e;   //this is different to tSCmdRfidReset
        unsigned char f;
        unsigned char g;
        unsigned char reserved[8];
        unsigned short int crc;
    } CmdRfidResetUpload;



    printf("sizeof CmdRfidResetUpload = %d\n", sizeof(CmdRfidResetUpload));

    printf("sizeof RfidReset= %d\n", sizeof(tSCmdRfidReset));

    return 0;
}