Discussion: Misallocation

Understand how pointer variables affect memory allocation in C, particularly when using the sizeof operator. This lesson helps you identify common misallocation errors caused by using sizeof on pointers rather than on the structure type itself. Learn to correctly allocate and write data to files by referencing structure sizes instead of pointer sizes to avoid incomplete data writes and errors in your C programs.

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Run the code
- Understanding the output
  - Explanation
    - Solution

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

int main()
{
  struct raw { int value; char string[32]; };
  FILE *outfile;
  struct raw *data;
  /* allocate and fill the structure */
  data = malloc( sizeof(struct raw) );
  data->value = 60;
  strcpy( data->string, "This is a string\n" );
  /* open a file and save the data */
  outfile = fopen("data.dat","w");
  
  if( outfile==NULL )
    exit(1);

  fwrite(data, sizeof(data), 1, outfile);
  fclose(outfile);
  puts("File written");
  /* clean up */
  free(data);

  return(0);
}

C code for the given puzzle

1.Before We Begin

2.Puzzles

3.Wrap Up

4.Appendix

Project

Discussion: Misallocation

Run the code

Understanding the output