Why doesn't valgrind detect a memory leak in m

The entire test code is contained in main.cpp as follows:

#include <iostream>

using std::cout;
using std::endl;

void f(int i) {
    int* pi = new int;

    *pi = i;

    std::cout << "*pi = " << *pi << std::endl;
}

int main(int argc, char *argv[]) {
    int i = 0;

    while (i < 10000) {
        f(i);
        ++i;
    }

    return 0;
}

I compile with no optimizations -O0 (from an Eclipse Qt project) with:

g++ -c -pipe -O0 -Wall -W -D_REENTRANT -DQT_NO_DEBUG -DQT_GUI_LIB -DQT_CORE_LIB -DQT_SHARED -I/usr/share/qt4/mkspecs/linux-g++ -I. -I/usr/include/qt4/QtCore -I/usr/include/qt4/QtGui -I/usr/include/qt4 -Irelease -o release/main.o main.cpp

then link as follows:

g++ -Wl,-O0 -o test release/main.o    -L/usr/lib -lQtGui -lQtCore -lpthread

I run the executable through valgrind and get the following output:

laptop:~/workspace/test$ valgrind --leak-check=yes test
==3939== Memcheck, a memory error detector
==3939== Copyright (C) 2002-2009, and GNU GPL'd, by Julian Seward et al.
==3939== Using Valgrind-3.6.0.SVN-Debian and LibVEX; rerun with -h for copyright info
==3939== Command: test
==3939== 
==3939== 
==3939== HEAP SUMMARY:
==3939==     in use at exit: 0 bytes in 0 blocks
==3939==   total heap usage: 1,387 allocs, 1,387 frees, 64,394 bytes allocated
==3939== 
==3939== All heap blocks were freed -- no leaks are possible
==3939== 
==3939== For counts of detected and suppressed errors, rerun with: -v
==3939== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 13 from 8)

I believe valgrind should report a memory leak rather than that no leaks are possible because of the heap memory allocated in the calls to new int

EDIT: Changed code above to use std::cout rather than qDebug() with the same result

If I compile and link the same code (from an Eclipse CDT project) with no Qt dependencies, valgrind detects the leak:

g++ -O0 -g3 -Wall -c -fmessage-length=0 -MMD -MP -MF"main.d" -MT"main.d" -o"main.o" "../main.cpp"

g++  -o"test2"  ./main.o   

==4604== HEAP SUMMARY:
==4604==     in use at exit: 40,000 bytes in 10,000 blocks
==4604==   total heap usage: 10,000 allocs, 0 frees, 40,000 bytes allocated
==4604== 
==4604== 40,000 bytes in 10,000 blocks are definitely lost in loss record 1 of 1
==4604==    at 0x402569A: operator new(unsigned int) (vg_replace_malloc.c:255)
==4604==    by 0x8048756: f(int) (main.cpp:7)
==4604==    by 0x80487BB: main (main.cpp:18)
==4604== 
==4604== LEAK SUMMARY:
==4604==    definitely lost: 40,000 bytes in 10,000 blocks
==4604==    indirectly lost: 0 bytes in 0 blocks
==4604==      possibly lost: 0 bytes in 0 blocks
==4604==    still reachable: 0 bytes in 0 blocks
==4604==         suppressed: 0 bytes in 0 blocks
==4604== 
==4604== For counts of detected and suppressed errors, rerun with: -v
==4604== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 19 from 8)

I'm using Kubuntu 10.04 32 bit and have tried both Debug and Release builds, what am I doing wrong or why doesn't valgrind report a memory leak when linked against Qt?

回答1:

The reason this happened is that the call to:

valgrind --leak-check=yes test

was actually running valgrind on /usr/bin/test which is a built in program that checks file types and compares values, all I needed was:

valgrind --leak-check=yes ./test

回答2:

I have replaced qDebug() with std::cout:

==2426== HEAP SUMMARY:
==2426==     in use at exit: 40,000 bytes in 10,000 blocks
==2426==   total heap usage: 10,000 allocs, 0 frees, 40,000 bytes allocated
==2426== 
==2426== LEAK SUMMARY:
==2426==    definitely lost: 39,996 bytes in 9,999 blocks

回答3:

Probably your compiler eliminate that code in the optimization, try compiling with -O0 (without optimization options).

As comment, with debian lenny with -O2, the leak is detected:

==20547== LEAK SUMMARY:
==20547==    definitely lost: 40,000 bytes in 10,000 blocks.
==20547==      possibly lost: 0 bytes in 0 blocks.
==20547==    still reachable: 516 bytes in 7 blocks.
==20547==         suppressed: 0 bytes in 0 blocks.
==20547== Rerun with --leak-check=full to see details of leaked memory.

The compiler:

    gcc version 4.3.2 (Debian 4.3.2-1.1)