Linux下如何检测内存泄漏

Valgrind通常用来成分析程序性能及程序中的内存泄露错误

一 Valgrind工具集简绍

Valgrind包含下列工具：

    1、memcheck：检查程序中的内存问题，如泄漏、越界、非法指针等。

    2、callgrind：检测程序代码的运行时间和调用过程，以及分析程序性能。

    3、cachegrind：分析CPU的cache命中率、丢失率，用于进行代码优化。

    4、helgrind：用于检查多线程程序的竞态条件。

    5、massif：堆栈分析器，指示程序中使用了多少堆内存等信息。

    6、lackey：

    7、nulgrind：

这几个工具的使用是通过命令：valgrand --tool=name 程序名来分别调用的，当不指定tool参数时默认是 --tool=memcheck

二 Valgrind工具详解

1.Memcheck

    最常用的工具，用来检测程序中出现的内存问题，所有对内存的读写都会被检测到，一切对malloc、free、new、delete的调用都会被捕获。所以，它能检测以下问题：

       1、对未初始化内存的使用；

       2、读/写释放后的内存块；

       3、读/写超出malloc分配的内存块；

       4、读/写不适当的栈中内存块；

       5、内存泄漏，指向一块内存的指针永远丢失；

       6、不正确的malloc/free或new/delete匹配；

       7、memcpy()相关函数中的dst和src指针重叠。

这些问题往往是C/C++程序员最头疼的问题，Memcheck能在这里帮上大忙。
例如：

    #include   
    #include   
    #include   
      
    void test()  
    {  
        int *ptr = malloc(sizeof(int)*10);  
      
        ptr[10] = 7; // 内存越界  
      
        memcpy(ptr +1, ptr, 5); // 踩内存  
      
      
        free(ptr);   
        free(ptr);// 重复释放  
      
        int *p1;  
        *p1 = 1; // 非法指针  
    }  
      
    int main(void)  
    {  
        test();  
        return 0;  
    }  

将程序编译生成可执行文件后执行：valgrind --leak-check=full ./程序名

输出结果如下：

    ==4832== Memcheck, a memory error detector  
    ==4832== Copyright (C) 2002-2010, and GNU GPL'd, by Julian Seward et al.  
    ==4832== Using Valgrind-3.6.1 and LibVEX; rerun with -h for copyright info  
    ==4832== Command: ./tmp  
    ==4832==   
    ==4832== Invalid write of size 4      // 内存越界  
    ==4832==    at 0x804843F: test (in /home/yanghao/Desktop/testC/testmem/tmp)  
    ==4832==    by 0x804848D: main (in /home/yanghao/Desktop/testC/testmem/tmp)  
    ==4832==  Address 0x41a6050 is 0 bytes after a block of size 40 alloc'd  
    ==4832==    at 0x4026864: malloc (vg_replace_malloc.c:236)  
    ==4832==    by 0x8048435: test (in /home/yanghao/Desktop/testC/testmem/tmp)  
    ==4832==    by 0x804848D: main (in /home/yanghao/Desktop/testC/testmem/tmp)  
    ==4832==   
    ==4832== Source and destination overlap in memcpy(0x41a602c, 0x41a6028, 5) // 踩内存  
    ==4832==    at 0x4027BD6: memcpy (mc_replace_strmem.c:635)  
    ==4832==    by 0x8048461: test (in /home/yanghao/Desktop/testC/testmem/tmp)  
    ==4832==    by 0x804848D: main (in /home/yanghao/Desktop/testC/testmem/tmp)  
    ==4832==   
    ==4832== Invalid free() / delete / delete[] // 重复释放  
    ==4832==    at 0x4025BF0: free (vg_replace_malloc.c:366)  
    ==4832==    by 0x8048477: test (in /home/yanghao/Desktop/testC/testmem/tmp)  
    ==4832==    by 0x804848D: main (in /home/yanghao/Desktop/testC/testmem/tmp)  
    ==4832==  Address 0x41a6028 is 0 bytes inside a block of size 40 free'd  
    ==4832==    at 0x4025BF0: free (vg_replace_malloc.c:366)  
    ==4832==    by 0x804846C: test (in /home/yanghao/Desktop/testC/testmem/tmp)  
    ==4832==    by 0x804848D: main (in /home/yanghao/Desktop/testC/testmem/tmp)  
    ==4832==   
    ==4832== Use of uninitialised value of size 4 // 非法指针  
    ==4832==    at 0x804847B: test (in /home/yanghao/Desktop/testC/testmem/tmp)  
    ==4832==    by 0x804848D: main (in /home/yanghao/Desktop/testC/testmem/tmp)  
    ==4832==   
    ==4832==   
    ==4832== Process terminating with default action of signal 11 (SIGSEGV) //由于非法指针赋值导致的程序崩溃  
    ==4832==  Bad permissions for mapped region at address 0x419FFF4  
    ==4832==    at 0x804847B: test (in /home/yanghao/Desktop/testC/testmem/tmp)  
    ==4832==    by 0x804848D: main (in /home/yanghao/Desktop/testC/testmem/tmp)  
    ==4832==   
    ==4832== HEAP SUMMARY:  
    ==4832==     in use at exit: 0 bytes in 0 blocks  
    ==4832==   total heap usage: 1 allocs, 2 frees, 40 bytes allocated  
    ==4832==   
    ==4832== All heap blocks were freed -- no leaks are possible  
    ==4832==   
    ==4832== For counts of detected and suppressed errors, rerun with: -v  
    ==4832== Use --track-origins=yes to see where uninitialised values come from  
    ==4832== ERROR SUMMARY: 4 errors from 4 contexts (suppressed: 11 from 6)  
    Segmentation fault  

从valgrind的检测输出结果看，这几个错误都找了出来。