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对大端小端的研究

第七根弦 2018 年 9 月 30 日 UC, Visual Studio 发表评论 (0)

简单的来说,通俗理解:
比如数据0x12345678
大端:地址由低到高,先放数据的高位,就是0x12,0x34,0x56,0x78;
小端:地址由低到高,先放数据的低位,就是0x78,0x56,0x34,0x12;

以下是验证代码(Windows、Linux均能跑通)
Windows平台需要在第一行加上#include “stdafx.h”

C++
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#include <stdio.h>
#include <string.h>
 
union Int
{
    char c[4];
    int  y;
};
union Long
{
#ifdef _WIN32
    char c[4];
#else
    char c[8];
#endif // _WIN32
    long  y;
};
union LongLong
{
    char c[8];
    long long y;
};
 
template<typename T>
void Print(T& f)
{
    unsigned char* p = (unsigned char*)&f;
    for (size_t i = 0; i < sizeof(T); ++i)
    {
        printf("%p %02x\n", p + i, *(p + i));
    }
    printf("\n\n");
}
 
int main()
{
    printf("int: %lu\n", sizeof(int));
    printf("long: %lu\n", sizeof(long));
    printf("long long: %lu\n", sizeof(long long));
 
    Int a;
    Long b;
    LongLong c;
    memset(&a, 0, sizeof(a));
    memset(&b, 0, sizeof(b));
    memset(&c, 0, sizeof(c));
 
    a.y = 0x01234567;
#ifdef _WIN32
    b.y = 0x89abcdef;
#else
    b.y = 0x0123456789abcdef;
#endif // _WIN32
    c.y = 0x1122334455667788;
 
    printf("Int: %p\n", &a);
    printf("Long: %p\n", &b);
    printf("LongLong: %p\n", &c);
 
    Print(a);
    Print(b);
    Print(c);
    return 0;
}

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