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C Brain Teasers: Exercise Your Mind

Misallocation

Explore the concept of misallocation in C by analyzing a puzzle code snippet to predict its output. This lesson helps you deepen your understanding of memory allocation issues and improve your ability to interpret code behavior effectively.

We'll cover the following...

Puzzle code

Read carefully the code given below:

C
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main()
{
  struct raw { int value; char string[32]; };
  FILE *outfile;
  struct raw *data;
  data = malloc( sizeof(struct raw) );
  data->value = 60;
  strcpy( data->string, "This is a string\n" );
  outfile = fopen("data.dat","w");
  
  if( outfile==NULL )
    exit(1);
  fwrite(data, sizeof(data), 1, outfile);
  fclose(outfile);
  puts("File written");
  free(data);
  return(0);
}

Your task: Guess the output

Attempt the following test to assess your understanding.

Technical Quiz
1.

What will be the content of the file data.dat after running the above program?

A.

The integer value 60 followed by the string "This is a string".

B.

The file will contain the raw binary representation of the structure, including both the integer and the string.

C.

The file will contain only a small portion of memory (4 or 8 bytes), which is the size of the pointer data, not the structure.

D.

The file will be empty due to a write failure in the fwrite function.

1 / 1

Let's discuss the code and output together in the next lesson.