Valgrind1 is a command line suite of tools to check for memory leaks in code (among other things), especially in memory-unsafe languages like C or C++. It instruments the heap and checks when we allocate or free memory, then tells us what we didn’t free.

The basics

We need a valid executable before using Valgrind. It’s best practice to compile in a “debug” mode, whether in a Make or with compilers like G++. This allows the tool to show the function names and line numbers where errors occur (but the line number may not be entirely accurate):

  • make config="debug"
  • g++ -g filename.cpp -o exename

Then we use Valgrind on the executable with valgrind ./exename. The leak-check flag is an important tool to use. Memcheck is the main tool we use to check for errors in memory allocation and access.2

Other tools

  • Cachegrind simulates CPU cache accesses, including for L1 (instruction-level I1 and data-level D1) and L2 caches. The point of this is to check for cache misses in our code.
  • Massif profiles the heap and shows dynamic heap allocation at a given moment.
  • Helgrind is a tool to detect threading errors.
  • Callgrind is a profiler that is able to provide an exact call graph. It reports performance in number of instructions instead of actual execution time.

Flags

  • --leak-check=full: provide detailed information on the memory leaks instead of just a summary.
  • --log-file=file-name: save the output to the file specified.
  • --tool=: run Valgrind using a different tool than Memcheck.

Footnotes

  1. ”Memory leaks are a scam invented by Valgrind to sell more Valgrind.” - Nick

  2. ”The purpose of all or some of these tools won’t be clear to you at this stage of your programming career, but will be by the end of your undergraduate degree.” - Quick start document for Valgrind, ECE297.