c - 将文件内容传递到内存时出现错误

Question

我想知道为什么当我认为我调用函数来正确加载时，看来 fread 无法正确读入我的内存块，因此它创建了一个段错误[在加载函数中]!请指出正确的方法

link代码是

#include <math.h>
#include <signal.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <strings.h>

bool load(FILE* file, char** content, size_t* length);

int main()
{
    // opens file
    FILE * file = fopen("test.txt", "r");

    // initialises variables 
    char* content;
    size_t length;

    // sending arguments to load function
    bool receive = load(file, &content, &length);

    // debugging content
    printf("values of content: %s\n", content);

    // debugs length

    printf("values of content: %zu\n", length);

    // closes file
    fclose(file);

    // for success
    return 0;
}

bool load(FILE* file, char** content, size_t* length)
{

    {

    // proof checking for the existence of file
    if (file == NULL)
        {
            return false;
        }

    // perusing to end of file   
    fseek(file, 0, SEEK_END);

    // for approximation of size of file    
    size_t len = ftell(file);

    // returns cursor to beginning of file  
    fseek(file, 0, SEEK_SET);

    // apportions memory on heap for content of file
    * content = (char *) malloc (len + 1);

    // memory error checking

    if(*content == NULL)
    {
        printf("It's unfortunate\n");

    }
    // to read into content     
    fread(* content, sizeof(char), len, file);

    // null terminates content
    (* content)[len] = 0;

    // debugs content    
    printf(" content contains %s\n", * content);

    // debugs length    
    * length = len;

    printf(" length is %d\n", * length);

    // if success 
    return true;

    }

    // if fail 
    return false;
}

谢谢

Answer 1

您需要检查文件是否正常打开

  FILE * file = fopen("test.txt", "r");
  if(file == NULL)
  {
      perror("failed to open file: ");
      exit(1);
  }

其次，你的加载函数返回 false 表示失败，但你没有检查它。做

 bool receive = load(file, &content, &length);
 if(!receive)
 {
     fprintf(stderr, "failed to read file");
     exit(1);
 }

你所做的事情

  if(*content == NULL)
    {
        printf("It's unfortunate\n");

    }

但是无论如何都要继续。你应该这样做

 if(*content == NULL)
    {
        printf("It's unfortunate\n");
        return false;
    }

一般来说，您不会检查您调用的任何函数的返回，fseek、ftell、fread，....当您的程序失败时，您不应该感到惊讶。是的，这是一个无聊的过程，但这就是 C 大陆的方式