我如何从C中的文件中读取

Question

How do I read from a file using this function?

#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;
}

I'm trying to implement to the following guidelines:

• 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

You pretty much included the answer in your question:

1. Allocate a char buffer of size length +1.

2. Open the file filename , in read only mode. If you fail to open the file, deallocate the buffer and return

3. Read length characters into the buffer, inserts a null character (\\0) in the last position, close the file and return a pointer to the buffer.

4. If you fail to read length characters, deallocate the buffer memory, close the file, and return NULL.