c - 我如何从C中的文件中读取

Question

如何使用此函数读取文件？

#include <stdio.h>

char* read_from_file (const char* filename, size_t length)
{
  //I have this so far
  fp = fopen(filename,"r"); // read mode

  if( fp == NULL )
  {
      perror("Error while opening the file.\n");
      exit(EXIT_FAILURE);
  }

  /* what goes in here? */

  return NULL;
}

我正在尝试实现以下准则:

• It allocates a char buffer of size length+1.

• It opens file filename, in read only mode. When it fails to open the file, it deallocates the buffer memory

• It reads length characters into the buffer, inserts a null character (\0) in the last position, closes the file and returns a pointer to the buffer. When it fails to read length characters, it deallocates the buffer memory, closes the file and returns NULL.

Answer 1

您几乎在问题中包含了答案:

1. 分配大小为 length+1 的字符缓冲区。

2. 以只读模式打开文件filename。如果打开文件失败，则释放缓冲区并返回

3. 将 length 个字符读入缓冲区，在最后一个位置插入一个空字符 (\0)，关闭文件并返回指向缓冲区的指针。

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4. 如果读取length个字符失败，则释放缓冲存储器，关闭文件，并返回NULL。