CERT C++: FIO42-C

Close files when they are no longer needed

expand all in page

Description

Rule Definition

Close files when they are no longer needed.¹

Polyspace Implementation

The rule checker checks for Resource leak.

Examples

expand all

Resource leak

Issue

Resource leak occurs when you open a file stream by using a FILE pointer but do not close it before:

The end of the pointer’s scope.
Assigning the pointer to another stream.

Risk

If you do not release file handles explicitly as soon as possible, a failure can occur due to exhaustion of resources.

Fix

Close a FILE pointer before the end of its scope, or before you assign the pointer to another stream.

Example - FILE Pointer Not Released Before End of Scope

#include <stdio.h>

void func1( void ) {
    FILE *fp1;
    fp1 = fopen ( "data1.txt", "w" );
    fprintf ( fp1, "*" );

    fp1 = fopen ( "data2.txt", "w" ); //Noncompliant
    fprintf ( fp1, "!" );
    fclose ( fp1 );
}

In this example, the file pointer fp1 is pointing to a file data1.txt. Before fp1 is explicitly dissociated from the file stream of data1.txt, it is used to access another file data2.txt.

Correction — Release FILE Pointer

One possible correction is to explicitly dissociate fp1 from the file stream of data1.txt.

#include <stdio.h>

void func1( void ) {
    FILE *fp1;
    fp1 = fopen ( "data1.txt", "w" );
    fprintf ( fp1, "*" );
    fclose(fp1);

    fp1 = fopen ( "data2.txt", "w" );                  
    fprintf ( fp1, "!" );
    fclose ( fp1 );
}

Check Information

Group: 07. Input Output (FIO)

Version History

Introduced in R2019a

expand all

R2023a: File handling functions that return integer file descriptors supported

The rule checker covers file opening and closing using the open() and close() functions.

¹ This software has been created by MathWorks incorporating portions of: the “SEI CERT-C Website,” © 2017 Carnegie Mellon University, the SEI CERT-C++ Web site © 2017 Carnegie Mellon University, ”SEI CERT C Coding Standard – Rules for Developing safe, Reliable and Secure systems – 2016 Edition,” © 2016 Carnegie Mellon University, and “SEI CERT C++ Coding Standard – Rules for Developing safe, Reliable and Secure systems in C++ – 2016 Edition” © 2016 Carnegie Mellon University, with special permission from its Software Engineering Institute.

ANY MATERIAL OF CARNEGIE MELLON UNIVERSITY AND/OR ITS SOFTWARE ENGINEERING INSTITUTE CONTAINED HEREIN IS FURNISHED ON AN "AS-IS" BASIS. CARNEGIE MELLON UNIVERSITY MAKES NO WARRANTIES OF ANY KIND, EITHER EXPRESSED OR IMPLIED, AS TO ANY MATTER INCLUDING, BUT NOT LIMITED TO, WARRANTY OF FITNESS FOR PURPOSE OR MERCHANTABILITY, EXCLUSIVITY, OR RESULTS OBTAINED FROM USE OF THE MATERIAL. CARNEGIE MELLON UNIVERSITY DOES NOT MAKE ANY WARRANTY OF ANY KIND WITH RESPECT TO FREEDOM FROM PATENT, TRADEMARK, OR COPYRIGHT INFRINGEMENT.

This software and associated documentation has not been reviewed nor is it endorsed by Carnegie Mellon University or its Software Engineering Institute.