linux recv返回-1

#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <sys/socket.h>

int main() {
    int sockfd;
    char buffer[1024];
    ssize_t bytes_received;

    // 假设 sockfd 已经正确初始化并连接到服务器

    bytes_received = recv(sockfd, buffer, sizeof(buffer), 0);
    if (bytes_received == -1) {
        perror("recv failed");
        // 或者使用
        fprintf(stderr, "recv failed: %s\n", strerror(errno));
    }

    return 0;
}

struct timeval timeout;
timeout.tv_sec = 5;  // 5秒超时
timeout.tv_usec = 0;

if (setsockopt(sockfd, SOL_SOCKET, SO_RCVTIMEO, (char *)&timeout, sizeof(timeout)) < 0) {
    perror("setsockopt failed");
}

bytes_received = recv(sockfd, buffer, sizeof(buffer), 0);
if (bytes_received == -1) {
    if (errno == ETIMEDOUT) {
        fprintf(stderr, "recv timed out\n");
    } else {
        perror("recv failed");
    }
}