(Q) Exercising valgrind¶

Note

Valgrind works in Linux desktop and in Linux computers, but most probably not in Mac nor Windows (or installing valgrind in these computers is impossible).

However, with Mac you can use valgrind via ssh as follows: In Mac command line, write the command:

ssh user_id@linux-desktop.tuni.fi

where user_id shall be replaced with your own user id. If you are asked ”Are you sure you want to continue …”, you can answer ”yes”. After that continue as told below at Executing ``valgrind`` on the command line.

Goal: I will learn to use valgrind for tracking the problems with memory management, and to interpret the output of valgrind.

This is important because, in the remaining projects, one requirement is that the submitted program has no problems with memory management. You are supposed to make sure that there are none by using valgrind during the test phase.

Instructions: Retrieve the code template: templates/09/valgrind/ -> student/09/valgrind/.

Let us examine this small program. You can see several problems to do with memory management right away:

#include <iostream>

using namespace std;

int main() {
    int number1;
    int number2 = 111;
    int *ptr1 = new int;
    int *ptr2 = new int(222);

    cout << number1 << " "
         << number2 << " "
         << *ptr1 << " "
         << *ptr2 << endl;

    delete ptr1;

    *ptr1 = 333;
}

The next two subsections give instructions to use valgrind both in Qt Creator and in command line. If possible, you can try both of these environments and compare them with each other.

Executing `valgrind` in Qt Creator¶

In Qt Creator, open the project you moved into the directory student/09/valgrind/.

If you want, you can execute the program. In the Application Output window, there should be the output ”exited with code 0”, that is, the execution of the program finished with the return value EXIT_SUCCESS, which means that everything went well (despite the program containing basically nothing but errors). Please note that when a program has as many problems with memory management as does our example program, it is not guaranteed that it will execute without hiccups. When the personnel created the assignment, it was possible to execute the program all the way to the end with the compiler installed on linux-desktop, but we cannot guarantee that it works similarly in all environments.

Execute valgrind by selecting Analyze > Valgrind Memory Analyzer. The program starts, but this time, the Application Output window will contain the output ”Analyzing finished”.

Also, Qt Creator opens the window Memcheck, and in its black top bar, it is supposed to say ”Memory Analyzer Tool finished, 8 issues were found”. We will examine the contents of that window in this assignment. If your Qt Creator shows nothing below the titles Issue and Location, click the filter icon located in the black top bar of the window and put a check on ”External Errors”. This will make the 8 problems valgrind found appear on the list.

There are two columns in the Memcheck window of Qt Creator: Issue and Location. There are two ways to access the Location column after clicking a downwards arrow to open one of the long lines and have a look at its contents:

by scrolling the bar at the bottom of the Memcheck window to the right.
by moving the cursor over the line where the Location column of interest to you is, and waiting until you see a box containing Location, in case the chosen line has data in the Location column.

(Q) Exercising valgrind¶

Executing valgrind in Qt Creator¶

Executing valgrind on the command line¶

Executing `valgrind` in Qt Creator¶

Executing `valgrind` on the command line¶