客户端发送一串小写字符串给服务端，服务端接受后将字符串转为大写，然后发给客户端，写出这个过程的C++的程序，包括客户端的程序和服务端的程序

以下是基于TCP的C语言客户端和服务端代码，实现了将小写字符串转换为大写字符串的功能。

客户端代码：

#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;
    struct sockaddr_in serv_addr;
    char message[BUF_SIZE];

    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_addr, 0, sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_addr.s_addr = inet_addr(argv[1]);
    serv_addr.sin_port = htons(atoi(argv[2]));

    if (connect(sock, (struct sockaddr*)&serv_addr, sizeof(serv_addr)) == -1) {
        error_handling("connect() error");
    }

    printf("Input lowercase string: ");
    fgets(message, BUF_SIZE, stdin);
    write(sock, message, strlen(message));

    int str_len = read(sock, message, BUF_SIZE-1);
    if (str_len == -1) {
        error_handling("read() error");
    }

    printf("Uppercase string: %s", message);

    close(sock);
    return 0;
}

void error_handling(char *message) {
    fputs(message, stderr);
    fputc('\n', stderr);
    exit(1);
}

服务端代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <ctype.h>

#define BUF_SIZE 1024

void error_handling(char *message);

int main(int argc, char *argv[]) {
    int serv_sock, clnt_sock;
    struct sockaddr_in serv_addr, clnt_addr;
    socklen_t clnt_addr_size;
    char message[BUF_SIZE];

    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_addr, 0, sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
    serv_addr.sin_port = htons(atoi(argv[1]));

    if (bind(serv_sock, (struct sockaddr*)&serv_addr, sizeof(serv_addr)) == -1) {
        error_handling("bind() error");
    }

    if (listen(serv_sock, 5) == -1) {
        error_handling("listen() error");
    }

    clnt_addr_size = sizeof(clnt_addr);
    clnt_sock = accept(serv_sock, (struct sockaddr*)&clnt_addr, &clnt_addr_size);
    if (clnt_sock == -1) {
        error_handling("accept() error");
    }

    int str_len = read(clnt_sock, message, BUF_SIZE);
    if (str_len == -1) {
        error_handling("read() error");
    }

    for (int i = 0; i < str_len; ++i) {
        message[i] = toupper(message[i]);
    }

    write(clnt_sock, message, str_len);

    close(clnt_sock);
    close(serv_sock);
    return 0;
}

void error_handling(char *message) {
    fputs(message, stderr);
    fputc('\n', stderr);
    exit(1);
}