Using valgrind

1. The valgrind utility can be used to detect memory problems (e.g., dynamically-allocated memory problems, accessing uninitialized variables).
2. To use valgrind make sure you compile your code with the -g option.
3. The command you should execute (assuming a.out is the executable) is:
   valgrind   --track-origins=yes   --leak-check=full   --show-leak-kinds=all   -s   a.out
4. If you replace the -s option with -q, you will only see valgrind output if there are any errors.
   valgrind   --track-origins=yes   --leak-check=full   --show-leak-kinds=all   -q   a.out
5. You should create an alias (similar to what you may have done with gcc) for the above command(s).
6. You can use valgrind with input/output redirection as well. The following illustrates how to run valgrind with the a.out executable, input from public01.in and placing the output in the file my_out.output
   
   valgrind a.out < public01.in > my_output.out

Examples

The following illustrates the information valgrind generates when we have not freed dynamically-allocated memory.

            ==2845066== 8 bytes in 1 blocks are definitely lost in loss record 1 of 2
            ==2845066==    at 0x484482F: malloc (vg_replace_malloc.c:431)
            ==2845066==    by 0x401269: create_photo (photo_album.c:16)
            ==2845066==    by 0x401502: add_photo_to_album (photo_album.c:80)
            ==2845066==    by 0x4011D4: main (public03.c:11)
            ==2845066==
            ==2845066== 12 bytes in 1 blocks are definitely lost in loss record 2 of 2
            ==2845066==    at 0x484482F: malloc (vg_replace_malloc.c:431)
            ==2845066==    by 0x401269: create_photo (photo_album.c:16)
            ==2845066==    by 0x401502: add_photo_to_album (photo_album.c:80)
            ==2845066==    by 0x4011BE: main (public03.c:10)
        

The following illustrates the information valgrind generates when we tried to access uninitialized memory allocated in the heap.

            ==2846814== Use of uninitialised value of size 8
            ==2846814==    at 0x48D156B: _itoa_word (in /usr/lib64/libc.so.6)
            ==2846814==    by 0x48EB11B: __vfprintf_internal (in /usr/lib64/libc.so.6)
            ==2846814==    by 0x48D74DE: printf (in /usr/lib64/libc.so.6)
            ==2846814==    by 0x401225: main (public03.c:17)
            ==2846814==  Uninitialised value was created by a heap allocation
            ==2846814==    at 0x484482F: malloc (vg_replace_malloc.c:431)
            ==2846814==    by 0x4011A6: main (public03.c:9)
        

The following illustrates the information valgrind generates when we tried to access uninitialized memory allocated in the stack.

            ==2846814== Use of uninitialised value of size 8
            ==2846814==    at 0x48D156B: _itoa_word (in /usr/lib64/libc.so.6)
            ==2846814==    by 0x48EB11B: __vfprintf_internal (in /usr/lib64/libc.so.6)
            ==2846814==    by 0x48D74DE: printf (in /usr/lib64/libc.so.6)
            ==2846814==    by 0x40120E: main (public03.c:16)
            ==2846814==  Uninitialised value was created by a stack allocation
            ==2846814==    at 0x401186: main (public03.c:6)            
        

Additional Information and Options You May Want to Try

• The valgrind -h shows valgrind options.
• The -v option shows miscellaneous extra information.
• The --show-mismatched-frees=yes option shows frees that don't match the allocator.
• For full information while looking for uninitialized values you should use the --track-origins=yes option.
• For details associated with leaked memory use the --leak-check=full.
• Reference: http://www.cprogramming.com/debugging/valgrind.html

Options for a Mac

In a Mac you could try the leaks command (e.g., leaks --atExit -- a.out). Additional information at https://computerscience.chemeketa.edu/guides/valgrind/leaks/.

Web Accessibility

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