c - Why does valgrind not show the obvious leaks in my program?

Question

Closed. This question needs debugging details. It is not currently accepting answers. question from:https://stackoverflow.com/questions/65890459/why-does-valgrind-not-show-the-obvious-leaks-in-my-program

Answer 1

After all those comments, the answer is kind of silly...

Your screenshot shows you ran valgrind ./substitution, without passing any command line arguments to your program. When this happens it prints Usage: ./substitution key and exits without doing anything further; in particular without calling cipher() and thus without ever calling malloc(). So of course there is no memory leak in this case.

If you run the program with a key argument on the command line, and give it some input, you should see valgrind report the memory leak:

==15815== 
==15815== HEAP SUMMARY:
==15815==     in use at exit: 54 bytes in 2 blocks
==15815==   total heap usage: 4 allocs, 2 frees, 2,102 bytes allocated
==15815== 
==15815== LEAK SUMMARY:
==15815==    definitely lost: 54 bytes in 2 blocks
==15815==    indirectly lost: 0 bytes in 0 blocks
==15815==      possibly lost: 0 bytes in 0 blocks
==15815==    still reachable: 0 bytes in 0 blocks
==15815==         suppressed: 0 bytes in 0 blocks
==15815== Rerun with --leak-check=full to see details of leaked memory

Although in principle a compiler could optimize out the malloc calls, in my tests with gcc and clang with -O3, I couldn't find any indication of them actually doing so.