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In this noncompliant code example the printf() function is called after the stdin the stdout stream is closed.

#include <stdio.h>
 
int close_stdinstdout(void) {
  if (fclose(stdinstdout) !== 0) {
    return -1;
  }
  else { 
    printf("stdinstdout successfully closed.\n");
  }
  return 0;
}

Compliant Solution

In this compliant solution, stdin stdout is not used again after it is closed.  This  This must remain true for the remainder of the program. 

#include <stdio.h>
 
int close_stdinstdout(void) {
  if (fclose(stdinstdout) =!= 0) {
    return -1;
  }

  else {
   
  fprintf(stderr, "stdinstdout successfully closed.\n");
  }
  return 0;
}

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Risk Assessment

Using the value of a pointer to a FILE object after the associated file is closed is undefined behavior.

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Search for vulnerabilities resulting from the violation of this rule on the CERT website. 

Bibliography

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