因为几天我坚持与我的一个应用程序的测试，我不能修复。所以我决定为我的测试写一个测试。。
我想分配内存，观察使用中内存的增长，然后再次释放内存。我希望分配的内存不再使用，对吗？
我正在使用Mac OSX（10.6.8）和gcc（GCC）4.2.1
所以我写了这个测试：

void testMemoryFreeCheck(){
    puts("- test Memory Free Check  -");
    puts("- ----------------------- -");
    puts("- This test takes a while -");
    puts("");
    struct rusage rus;
    getrusage(RUSAGE_SELF, &rus);

    // Things befor we want to mature. 
    char *holder[10000];
    char *bigHolder;
    int loops =  10000;
    int i;

    // Variables used for tests. 
    long int afterFirstTestKiloByte = 0;
    long int afterSecondTestKiloByte = 0;
    long int afterThirdTestKiloByte = 0;
    long int afterForuthTestKiloByte = 0;

    getrusage(RUSAGE_SELF, &rus);
    long int initialKiloByte = rus.ru_maxrss;
    printf("Initial KB Used: %ld\n", initialKiloByte);

    // a adder to proof that we get it write
    char add = "A";
    getrusage(RUSAGE_SELF, &rus);
    long int afterAddKiloByte = rus.ru_maxrss;
    printf("After a char add KB Used: %ld\n", initialKiloByte);
    getrusage(RUSAGE_SELF, &rus);
    long int growingKiloByte = rus.ru_maxrss;

    // This loop should do nothing.
    for(i=0; i<loops; ++i){
        printf(".");
    }
    puts("");
    getrusage(RUSAGE_SELF, &rus);
    afterFirstTestKiloByte = rus.ru_maxrss;
    printf("First Test should be 0 : %ld\n", (afterFirstTestKiloByte - afterAddKiloByte));
    CU_ASSERT_TRUE( (afterFirstTestKiloByte - afterAddKiloByte) == 0);

    // This loop should free all allocated space.
    for(i=0; i<(loops * 128); ++i){
        char *tmp = malloc(1024 * 1024);
        free(tmp);
    }

    getrusage(RUSAGE_SELF, &rus);
    afterSecondTestKiloByte = rus.ru_maxrss;
    printf("Second Test should be 0 (4096 is ok for some reasons): %ld\n", (afterSecondTestKiloByte - afterAddKiloByte));
    CU_ASSERT_TRUE( (afterSecondTestKiloByte - afterAddKiloByte) <= 4096);

    // This loop should increase the allocated space.
    for(i=0; i<loops; ++i){
        holder[i] = malloc(1024 * 1024);
    }
    getrusage(RUSAGE_SELF, &rus);
    afterThirdTestKiloByte = rus.ru_maxrss;
    printf("Third Test should be grater than 0 : %ld\n", (afterThirdTestKiloByte - afterAddKiloByte));
    CU_ASSERT_TRUE( (afterThirdTestKiloByte - afterAddKiloByte) > 0);

    // now free the memmory and get back to the initial value
    for(i=0; i<loops; ++i){
        free(holder[i]);
    }  
    getrusage(RUSAGE_SELF, &rus);
    afterForuthTestKiloByte = rus.ru_maxrss;
    printf("Forth Test should be reset to 0 : %ld\n", (afterForuthTestKiloByte - afterAddKiloByte));
    CU_ASSERT_TRUE( (afterThirdTestKiloByte - afterAddKiloByte) == 0);

    puts("- ----------------------- -");
}

我的输出是：

- test Memory Free Check  -
- ----------------------- -
- This test takes a while -

Initial KB Used: 458752
After a char add KB Used: 458752
[...]
First Test should be 0 : 0
Second Test should be 0 (4096 is ok for some reasons): 4096
Third Test should be grater than 0 : 1601536
Forth Test should be reset to 0 : 1601536
- ----------------------- -

我有两个问题到现在还不能解释清楚：
1.为什么第二个测试是4096而不是0？
1.为什么第四次测试没有0？
第四个测试把我吓坏了。请看一下，也许你可以解释如何测试一个空闲内存调用。我假设内存管理器不杀死字节，但重用它，所以内存将感染rus.ru_maxrss。但我如何测试免费？