UNIX网络编程 套接字编程介绍

 

 

 

 

 

打印当前机器是小头派还是大头派类型

注意，如果没有加这两个头文件

#include <stdio.h>

#include <stdlib.h>

编译时候会报  警告：隐式声明与内建函数‘printf’不兼容   这个错误

编译: gcc -o byteorder byteorder.c

#include <stdio.h>
#include <stdlib.h>

int main(int argc,char **argv) {
    union {
        short s;
        char c[sizeof(short)];
    }un;

    un.s=0x0102;
    if(sizeof(short) ==2) {
        if(un.c[0]==1 && un.c[1]==2) {
            printf("big-endian\n");
        }
        else if(un.c[0]==2 && un.c[1]==1) {
            printf("little-endian\n");
        }
        else {
            printf("unknown\n");
        }
    }
    else {
        printf("sizeof(short) = %d\n",sizeof(short));
    }
    return 0;

}

 

10进制ip到二进制转换的例子

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
int main (void) {
    char IPdotdec[20]; //存放点分十进制IP地址
    struct in_addr s; // IPv4地址结构体
    // 输入IP地址
    printf("Please input IP address: ");
    scanf("%s", IPdotdec);
    // // 转换
    inet_pton(AF_INET, IPdotdec, (void *)&s);
    printf("inet_pton: 0x%x\n", s.s_addr); // 注意得到的字节序
    //  反转换
    inet_ntop(AF_INET, (void *)&s, IPdotdec, 16);
    printf("inet_ntop: %s\n", IPdotdec);

}

 

 

一次读取n个字节的readn函数

#include <stdio.h>
#include <stdlib.h>
#include <netinet/in.h>
#include <unistd.h>
#include <fcntl.h>

ssize_t readn(int fd,void *vptr, size_t n) {
    size_t nleft;
    ssize_t nread;
    char *ptr;

    ptr = vptr;
    nleft = n;
    while(nleft > 0) {
        if( (nread=read(fd,ptr,nleft)) < 0) {
            if(nread > 0) {
                nread = 0;
            } else {
                return -1;
            }
        }
        else if(nread == 0) {
            break;
        }
        nleft -= nread;
        ptr += nread;   
    }       
    return (n-nleft);
}           
                    
int main(int argc, char **argv) {
              
    int r_fd=open("/data0/test/test.log",O_RDONLY);
    char buf[100];
    readn(r_fd,buf,20); 
    printf("%s\n",buf);
    
    return 0;
}

 

一次写入n个字节的writen函数

#include <stdio.h>
#include <stdlib.h>
#include <netinet/in.h>
#include <unistd.h>
#include <fcntl.h>


ssize_t writen(int fd, const void *vptr, size_t n) {
    size_t nleft;
    ssize_t nwritten;
    const char *ptr;

    ptr = vptr;
    nleft = n;
    while(nleft > 0) {
        if( (nwritten = write(fd,ptr,nleft)) <= 0) {
            if(nwritten <0) {
                nwritten = 0;
            }
            else {
                return -1;
            }
        }
        nleft -= nwritten;
        ptr += nwritten;
    }
    return n;
}

int main(int argc, char **argv) {
    int w_fd = open("/data0/test/write.log",O_WRONLY|O_CREAT,0755);
    writen(w_fd,"test he he",10);
    return 0;
}

 

每次读取一行的readline函数

#include <stdio.h>
#include <stdlib.h>
#include <netinet/in.h>
#include <unistd.h>
#include <fcntl.h>

ssize_t readline(int fd, void *vptr, size_t maxlen) {
    ssize_t n,rc;
    char c, *ptr;

    ptr = vptr;
    for(n=1;n<maxlen;n++) {
        if( (rc=read(fd,&c,1)) ==1) {
            *ptr++ = c;
            if(c=='\n') {
                break;
            }
        }
        else if(rc == 0) {
            *ptr = 0;
            return (n-1);
        }
        else {
            if(rc < 0) {
                continue;
            }
            return -1;
        }

    }
    *ptr = 0;
    return n;

}

int main(int argc, char **argv) {
    int r_fd=open("/data0/test/test.log",O_RDONLY);
    char buf[100];
    readline(r_fd,buf,20);
    printf("%s\n",buf);
    return 0;
}

 

 

参考

inet_pton函数