Question

I wrote this header file for a another main program. This file declares a struct_buffer struct that is used by the main function (somewhere else).

What I am trying to do is that when someone initialises a buffer with the buffer_init function, a pointer to the buffer is returned. The buffer would contain, an array of pointers, the current number of pointer in the buffer(size), and the file-pointer to a file to which the pointers stored in the buffer will be dumped.

The main program will call the add_to_buffer() function to add pointers to the buffer. This in turn calls the buffer_dump() function to dump the pointers in a file specified by the buffer->fp. At the end, I will call buffer_close() to close the file. However compiling it gives me several errors that I am unable to understand and get rid of.

The following is a code of header file in C, that I am trying to compile and it is giving me errors that I can’t understand.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define MAX_PTRS 1000

struct struct_buffer
{
    int size;
    File *fp;
    unsigned long long ptrs[MAX_PTRS];
};

//The struct_buffer contains the size which is the number of pointers in ptrs, fp is the file pointer to the file that buffer will write 
struct struct_buffer*
buffer_init(char *name)
{
    struct struct_buffer *buf = malloc(sizeof(struct struct_buffer));
    buf->size = 0;
    buf->fp = fopen(name,"w");
    return buf;
}

//This function dumps the ptrs to the file.
void
buffer_dump (struct struct_buffer *buf)
{
  int ctr=0;
  for(ctr=0; ctr < buf->size ; ctr++)
  {
    fprintf(buf->fp, "%llx\n",buf->ptrs[ctr]);
  }
}

//this function adds a pointer to the buffer
void
add_to_buffer (struct struct_buffer *buf, void *ptr)
{
 if(buf->size >= MAX_PTRS)
 {
  buffer_dump(buf);
  buf->size=0;
 }
 buf->ptrs[(buf->size)++] = (unsigned long long)ptr;
}

//this functions closes the file pointer
void
buffer_close (struct struct_buffer *buf)
{
 fclose(buf->fp);
}                          

The above code on compilation gives me the following errors. I could not understand the problem. Please explain to me what the trouble is.

buffer.h:10: error: expected specifier-qualifier-list before 'File'
buffer.h: In function 'buffer_init':
buffer.h:19: error: 'struct struct_buffer' has no member named 'fp'
buffer.h: In function 'buffer_dump':
buffer.h:29: error: 'struct struct_buffer' has no member named 'fp'
buffer.h:29: error: 'struct struct_buffer' has no member named 'ptrs'
buffer.h: In function 'add_to_buffer':
buffer.h:40: error: 'struct struct_buffer' has no member named 'ptrs'
buffer.h: In function 'buffer_close':
buffer.h:46: error: 'struct struct_buffer' has no member named 'fp'

Answer 1

File is not defined. The correct type you are looking for is FILE.

struct struct_buffer
{
    int size;
    FILE *fp; // <---------
    unsigned long long ptrs[MAX_PTRS];
};

The rest of your errors appear to be a product of this error, so this should be your only fix.