……
while ((str_len = read(clnt_sock, messag, 1024)) != 0)write(clnt_sock, messag, str_len);
……

……
write(sock, message, strlen(message));
str_len = read(sock, message, 1024 - 1);
……

……
while (1)
{fputs("Input message(Q to quit):", stdout);fgets(message, 1024, stdin);if (!strcmp(message, "q\n") || !strcmp(message, "Q\n"))break;write(sock, message, strlen(message));str_len = read(sock, message, 1024 - 1);message[str_len] = 0;printf("Message from server:%s", message);
}
……

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#define BUF_SIZE 1024
void error_handling(char *message);int main(int argc, char *argv[])
{int sock;char message[BUF_SIZE];int str_len, recv_len, recv_cnt;struct sockaddr_in serv_adr;if (argc != 3){printf("Usage:%s<IP><port>\n", argv[0]);exit(1);}sock = socket(PF_INET, SOCK_STREAM, 0);if (sock == -1)error_handling("socket()error");memset(&serv_adr, 0, sizeof(serv_adr));serv_adr.sin_family = AF_INET;serv_adr.sin_addr.s_addr = inet_addr(argv[1]);serv_adr.sin_port = htons(atoi(argv[2]));if (connect(sock, (struct sockaddr *)&serv_adr, sizeof(serv_adr)) == -1)error_handling("connect()error");elseputs("Connected..........");while (1){fputs("Input message(Q to quit):", stdout);fgets(message, BUF_SIZE, stdin);if (!strcmp(message, "q\n") || !strcmp(message, "Q\n"))break;str_len = write(sock, message, strlen(message));recv_len = 0;while (recv_len < str_len){recv_cnt = read(sock, &message[recv_len], BUF_SIZE - 1);if (recv_cnt == -1)error_handling("read()error!");recv_len += recv_cnt;}message[recv_len] = 0;printf("Message from server:%s", message);}close(sock);return 0;
}void error_handling(char *message)
{fputs(message, stderr);fputc('\n', stderr);exit(1);
}

while (recv_len != str_len)
{……
}

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#define BUF_SIZE 1024
#define RLT_SIZE 4
#define OPSZ 4
void error_handling(char *message);
int main(int argc, char *argv[])
{int sock;char opmsg[BUF_SIZE];int result, opnd_cnt, i;struct sockaddr_in serv_adr;if (argc != 3){printf("Usage:%s <IP><port>\n", argv[0]);exit(1);}sock = socket(PF_INET, SOCK_STREAM, 0);if (sock == -1){error_handling("socket() error");}memset(&serv_adr, 0, sizeof(serv_adr));serv_adr.sin_family = AF_INET;serv_adr.sin_addr.s_addr = inet_addr(argv[1]);serv_adr.sin_port = htons(atoi(argv[2]));if (connect(sock, (struct sockaddr *)&serv_adr, sizeof(serv_adr)) == -1)error_handling("connect() error!");elseputs("Connected......");fputs("Operand count:", stdout);scanf("%d", &opnd_cnt);opmsg[0] = (char)opnd_cnt;for (i = 0; i < opnd_cnt; i++){printf("Operand %d:", i + 1);scanf("%d", (int *)&opmsg[i * OPSZ + 1]);}fgetc(stdin);fputs("Operator:", stdout);scanf("%c", &opmsg[opnd_cnt * OPSZ + 1]);write(sock, opmsg, opnd_cnt * OPSZ + 2);read(sock, &result, RLT_SIZE);printf("Operation result:%d\n", result);close(sock);return 0;
}
void error_handling(char *message)
{fputs(message, stderr);fputc('\n', stderr);exit(1);
}

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#define BUF_SIZE 1024
#define OPSZ 4
void error_handling(char *message);
int calculate(int opnum, int opnds[], char operator);int main(int argc, char *argv[])
{int serv_sock, clnt_sock;char opinfo[BUF_SIZE];int result, opnd_cnt, i;int recv_cnt, recv_len;struct sockaddr_in serv_adr, clnt_adr;socklen_t clnt_adr_sz;if (argc != 2){printf("Usage:%s<port>\n", argv[0]);exit(1);}serv_sock = socket(PF_INET, SOCK_STREAM, 0);if (serv_sock == -1)error_handling("socket() error");memset(&serv_adr, 0, sizeof(serv_adr));serv_adr.sin_family = AF_INET;serv_adr.sin_addr.s_addr = htonl(INADDR_ANY);serv_adr.sin_port = htons(atoi(argv[1]));if (bind(serv_sock, (struct sockaddr *)&serv_adr, sizeof(serv_adr)) == -1)error_handling("bind() error");if (listen(serv_sock, 5) == -1)error_handling("listen() error");clnt_adr_sz = sizeof(clnt_adr);for (i = 0; i < 5; i++){opnd_cnt = 0;clnt_sock = accept(serv_sock, (struct sockaddr *)&clnt_adr, &clnt_adr_sz);read(clnt_sock, &opnd_cnt, 1);recv_len = 0;while ((opnd_cnt * OPSZ + 1) > recv_len){recv_cnt = read(clnt_sock, &opinfo[recv_len], BUF_SIZE - 1);recv_len += recv_cnt;}result = calculate(opnd_cnt, (int *)opinfo, opinfo[recv_len - 1]);write(clnt_sock, (char *)&result, sizeof(result));close(clnt_sock);}close(serv_sock);return 0;
}
int calculate(int opnum, int opnds[], char op)
{int result = opnds[0], i;switch (op){case '+':for (i = 1; i < opnum; i++)result += opnds[i];break;case '-':for (i = 1; i < opnum; i++)result -= opnds[i];break;case '*':for (i = 1; i < opnum; i++)result *= opnds[i];break;}return result;
}
void error_handling(char *message)
{fputs(message, stderr);fputc('\n', stderr);exit(1);
}

# gcc op_server.c -o op_server
# ./op_server 8500

# gcc op_client.c -o op_client
# ./op_client 127.0.0.1 8500
Connected......
Operand count:3
Operand 1:1
Operand 2:2
Operand 3:3
Operator:+
Operation result:6
# ./op_client 127.0.0.1 8500
Connected......
Operand count:2
Operand 1:2
Operand 2:15
Operator:*
Operation result:30