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   -s   a.out
4. If you add the -q option and remove the -s option, you will only see valgrind output if there are any errors.
   valgrind   --track-origins=yes   --leak-check=full   -q   a.out
5. You should create an alias (similar to what you may have done with gcc) for the above command.

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

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