c - 尝试覆盖 'fopen()' 但 GCC 给出 "error: conflicting types for ' fopen'"

Question

My last question作为背景。我试图环绕“fopen()”，但 gcc 给了我这个错误，而“remove()”没有问题。

错误:“fopen”的类型冲突fopen(const char *路径名, const char *模式)^在 file_io_operation_interception.c:2:0 包含的文件中:/usr/include/stdio.h:272:14:注意:之前的“fopen”声明是这里extern FILE *fopen (const char *__restrict __filename,

这是代码。

#define _GNU_SOURCE
#include <stdio.h>
#include <dlfcn.h>
#include <errno.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>

#define PORT     8080
#define MAXLINE 1024

static int (*real_fopen)(const char *pathname, const char *mode) = NULL;
static int (*real_remove)(const char *filename) = NULL;
static int (*real_close)(int fd) = NULL;

__attribute__((constructor))
void
my_lib_init(void)
{

    real_fopen = dlsym(RTLD_NEXT,"fopen");
    real_remove = dlsym(RTLD_NEXT,"remove");
    real_close = dlsym(RTLD_NEXT,"close");
}

int
fopen(const char *pathname, const char *mode)
{
    int fd;

    // do whatever special stuff ...

    fd = real_fopen(pathname, mode);
    printf("open worked!\n");
    char message[200];
    char fidString[10];
    sprintf(fidString, "%d ", fd);
    strcat(message, fidString);
    strcat(message, pathname);
    sendMessage(message);
    // do whatever special stuff ...

    return fd;
}

int
remove(const char *filename)
{
    int ret;
    /*
    if (real_remove == NULL)
        real_remove = dlsym(RTLD_NEXT,"remove");
    */

    // do whatever special stuff ...
    printf("remove worked!\n");
    sendMessage("remove message sent");
    ret = real_remove(filename);

    // do whatever special stuff ...

    return ret;
}

int
close(int fd)
{
    int ret;
    /*
    if (real_close == NULL)
        real_close = dlsym(RTLD_NEXT,"close");
    */
    // do whatever special stuff ...
    printf("close worked!\n");
    ret = real_close(fd);
    // do whatever special stuff ...
    return ret;
}

int
sendMessage(char *message)
{
    int sockfd;
    struct sockaddr_in     servaddr;

    // Creating socket file descriptor
    if ( (sockfd = socket(AF_INET, SOCK_DGRAM, 0)) < 0 ) {
        perror("socket creation failed");
        exit(EXIT_FAILURE);
    }

    memset(&servaddr, 0, sizeof(servaddr));

    // Filling server information
    servaddr.sin_family = AF_INET;
    servaddr.sin_port = htons(PORT);
    servaddr.sin_addr.s_addr = INADDR_ANY;

    int n, len;

    sendto(sockfd, (const char *)message, strlen(message),
        MSG_CONFIRM, (const struct sockaddr *) &servaddr,
            sizeof(servaddr));
    printf("message sent\n");
    close(sockfd);
    return 0;
}

“remove()”函数工作正常，但“fopen()”则不行。它们都在 stdio.h 中声明。但是，为什么会出现这种差异呢？

Answer 1

我已经找到解决办法了。 “fopen()”的返回值应该是FILE *，但我错误地使用了int。