Usage of Valgrind

• Memory bugs are hard to find, until strings some variables changes values randomly.
• Valgrind is a suite of profiling tools that allows you to check your code in a number of ways.
• Default one: the memcheck tool, it's also perhaps the most powerful one. It runs your code inside of a virtual machine. It then instruments all of the memory accesses that you are performing, and it double checks to make sure your pointer accesses are valid.

Installation example:

sudo apt-get install valgrind

• Make sure to add the -g flag to the compiler, which sets up debugging information.
• Also turn on -Wall -Werror so your compiler can tell you what is wrong as much as possible.

First step is valgrind ./program to start off. The numbers between == at the beginning of each line is the Process ID Valgrind is currently working on.

Some flags to use:

--leak-check=full: Prints detailed info for each detected memory leak, where the memory was allocated, how big it is, and whether it's reachable or not.

--leak-check=summary: Only prints the final summary. Useful for quick checks.

--track-origins=yes: Traces the origin of uninitialized memory so you can see where in your code you forgot to initialize it.

--show-leak-kinds=all: By default, Valgrind only shows certain leak categories. With all, you'll see:

• Definitely lost: memory you 100% forgot to free.
• Indirectly lost: memory was only reachable through a block that's definitely lost.
• Possibly lost: Valgrind can't be sure, but the pointer situation looks sketchy (e.g., pointer arithmetic changed the address).
• Still reachable: memory is still pointed to at exit, so it isn't technically leaked. Often from static/global allocations or intentional caches.

--num-callers=<n>: Shows <n> stack frames for each error. Default: 12. More stack depth for messy call chains.

--error-limit=no: Disables the default limit on errors shown.

--quiet: Minimal output, useful in scripts or CI logs.

--gen-suppressions=yes: Generates suppression entries for false positives. For library code you can't change.

--log-file=<file>: Saves all output into a file.