編寫網路程式處除了要理解各種地址和必要的函式，還要檢測程式出錯。如果每次呼叫一個基本的socket函式都要判斷其結果是否正確，會給程式設計帶來麻煩。因此大多數都會定義包裹函式，對每一個基本socket函式進行封裝。下面是借鑑了《linux C程式設計一站式學習》中的程式碼進行整理：

#include <stdlib.h>
#include <errno.h>
#include <sys/socket.h>
#include <unistd.h>
#include <stdio.h>

#include "wrap.h"

void perr_exit(const char *s)
{
	perror(s);
	exit(1);
}

int Socket(int family, int type, int protocol)
{
	int n;

	if ( (n = socket(family, type, protocol)) < 0)
		perr_exit("socket error");
	return n;
}
void Connect(int fd, const struct sockaddr *sa, socklen_t salen)
{
	if (connect(fd, sa, salen) < 0)
		perr_exit("connect error");
}
void Bind(int fd, const struct sockaddr *sa, socklen_t salen)
{
	if (bind(fd, sa, salen) < 0)
		perr_exit("bind error");
}

void Listen(int fd, int backlog)
{
	if (listen(fd, backlog) < 0)
		perr_exit("listen error");
}
int Accept(int fd, struct sockaddr *sa, socklen_t *salenptr){int n;
again:
	if ( (n = accept(fd, sa, salenptr)) < 0) {
		if ((errno == ECONNABORTED) || (errno == EINTR))
			goto again;
		else
			perr_exit("accept error");
	}
	return n;
}
//有Readn就不用它了
ssize_t Read(int fd, void *ptr, size_t nbytes)
{
	ssize_t n;

again:
	if ( (n = read(fd, ptr, nbytes)) == -1) {
		if (errno == EINTR)
			goto again;
		else
			return -1;
	}
	return n;
}
//有Writen就不用它了
ssize_t Write(int fd, const void *ptr, size_t nbytes)
{
	ssize_t n;

again:
	if ( (n = write(fd, ptr, nbytes)) == -1) {
		if (errno == EINTR)
			goto again;
		else
			return -1;
	}
	return n;
}

void Close(int fd)
{
	if (close(fd) == -1)
		perr_exit("close error");
}
//讀n個位元組到prt中，返回實際讀到的位元組數，-1代表出錯
ssize_t Readn(int fd, void *vptr, size_t n)
{
    size_t nleft;
    ssize_t nread;
    char *ptr;
    ptr = vptr;
    nleft = n;//剩下nleft未讀
    while (nleft > 0) {
        if ( (nread = read(fd, ptr, nleft)) < 0) {
            if (errno == EINTR)
                nread = 0;
            else
                return -1;//出錯
        } else if (nread == 0)
                break;//讀完
        nleft -= nread;
        ptr += nread;
    }
    return n - nleft;//讀出的位元組數
}
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 && errno == EINTR)
                nwritten = 0;
            else
                return -1;
        }
    nleft -= nwritten;
    ptr += nwritten;
    }
    return n;
}