快捷導(dǎo)航

C++實現(xiàn)主機字節(jié)序和網(wǎng)絡(luò)字節(jié)序轉(zhuǎn)換示例

更新時間：2023年11月02日 11:37:11 作者：點墨

這篇文章主要為大家介紹了C++實現(xiàn)主機字節(jié)序和網(wǎng)絡(luò)字節(jié)序轉(zhuǎn)換示例詳解，有需要的朋友可以借鑒參考下，希望能夠有所幫助，祝大家多多進步，早日升職加薪

字節(jié)序問題

現(xiàn)代CPU一次至少能裝載4字節(jié)(32位機),即一個整數(shù)，這4個字節(jié)在內(nèi)存中的排列順序?qū)⒂绊懰闹?。這就是字節(jié)序問題。字節(jié)序分為大端字節(jié)序(big endian)和小端字節(jié)序(little endian)。

如上圖，大端字節(jié)序是指數(shù)據(jù)的高位存在內(nèi)存的低地址處，小端字節(jié)序是指數(shù)據(jù)的高位存在內(nèi)存的高地址處。

現(xiàn)代PC大多采用小端字節(jié)序

當(dāng)格式化的數(shù)據(jù)需要在兩臺使用不同字節(jié)序的主機進行傳遞時，接收端會錯誤的處理。解決的方法是:發(fā)送端將發(fā)送的數(shù)據(jù)轉(zhuǎn)換成大端字節(jié)序然后發(fā)送，接收端根據(jù)自己的字節(jié)序決定需不需要處理(小端轉(zhuǎn)換，大端不處理)。

在做網(wǎng)絡(luò)編程的時候，使用提供的庫即可進行轉(zhuǎn)換(linux庫,windows下是一樣的，頭文件有所區(qū)別)

#include <netinet/in.h>
unsigned long int _htonl(unsigned long int hostlong);
unsigned short int _htons(unsigned short int hostshort);
unsigned long int _ntohl(unsigned long int netlong);
unsigned short int _ntohs(unsigned short int netshort);

互換數(shù)據(jù)

如果平臺沒有提供這套，那么可以自己實現(xiàn)一下，原理很簡單，就是互換下數(shù)據(jù)

#include <stdint.h>
#define BigLittleSwap16(v) ((0xFF00 & (uint16_t)(v)) >> 8 | (0x00FF & (uint16_t)(v)) << 8)
#define BigLittleSwap32(v) ((0xFF000000 & (uint32_t)(v)) >> 24 | (0x00FF0000 & (uint32_t)(v)) >> 8 | (0x0000FF00 & (uint32_t)(v)) << 8 | (0x000000FF & (uint32_t)(v)) << 24) 
#define BigLittleSwap64(v) ((0xFF00000000000000 & (uint64_t)(v)) >> 56 |(0x00FF000000000000 & (uint64_t)(v)) >> 40 |(0x0000FF0000000000 & (uint64_t)(v) )>> 24 |(0x000000FF00000000 & (uint64_t)(v)) >> 8 |(0x00000000FF000000 & (uint64_t)(v)) << 8| (0x0000000000FF0000 & (uint64_t)(v)) << 24 | (0x000000000000FF00 & (uint64_t)(v) )<< 40 | (0x00000000000000FF & (uint64_t)(v) )<< 56 )
int isCPUBigEndian(){
    union Data{
        short val;
        char byte;
    } data;
    data.val = 0x0102;
    return (data.byte == 0x01);
}
unsigned long int _htonl(unsigned long int hostlong);
unsigned short int _htons(unsigned short int hostshort);
unsigned long int _ntohl(unsigned long int netlong);
unsigned short int _ntohs(unsigned short int netshort);
unsigned long int _htonl(unsigned long int hostlong){
    return isCPUBigEndian() ? hostlong : BigLittleSwap32(hostlong);
}
unsigned short int _htons(unsigned short int hostshort){
    return isCPUBigEndian() ? hostshort : BigLittleSwap16(hostshort);
}
unsigned long int _ntohl(unsigned long int netlong){
    return isCPUBigEndian() ? netlong : BigLittleSwap32(netlong);
}
unsigned short int _ntohs(unsigned short int netshort){
    return isCPUBigEndian() ? netshort : BigLittleSwap16(netshort);
}

測試

#include <netinet/in.h>
#include <stdio.h>
int main(int argc,const char*argv[]){
   long int v1 = 0x11223344;
   short int v2 = 0x1122;
   printf("the endian of system is:%s\n",isCPUBigEndian()?"Big Endian":"Little Endian");
   printf("htonl:%x , %x , %x\n",v1,htonl(v1),_htonl(v1));
   printf("htons:%x , %x , %x\n",v2,htons(v2),_htons(v2));
   printf("ntohl:%x , %x , %x\n",v1,ntohl(v1),_ntohl(v1));
   printf("ntohs:%x , %x , %x\n",v2,htons(v2),_htons(v2));
    return 0;
}

在linux下的測試結(jié)果如下圖