Valgrind检测使用未初始化的内存

一时失言乱红尘 2021-09-19 11:24 339阅读 0赞

**一 点睛**

对于位于程序中的不同段的变量，其初始值是不同的，全局变量和静态变量初始值为0，而局部变量和动态申请的变量，其初始值为随机值。如果程序使用了为随机数的变量，那么程序的行为就变得不可预期了。

**二 错误代码**

#include<iostream>
    using namespace std;
    int main(){
        int a[5];
        int i,s=0;
        a[0]=a[1]=a[3]=a[4]=0;
        for(i=0;i<5;i++)
                s=s+a[i];
        if(s==33)
                cout<<"sum is 33"<<endl;
        else
                cout<<"sum is not 33"<<endl;
        return 0;
    }

**三 编译并运行**

[root@localhost charpter05]# g++ -g 0509test.cpp -o 0509
    [root@localhost charpter05]# ./0509
    sum is not 33

**四 用Valgrind检测使用未初始化的内存**

[root@localhost charpter05]# valgrind ./0509
    ==17792== Memcheck, a memory error detector
    ==17792== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
    ==17792== Using Valgrind-3.15.0 and LibVEX; rerun with -h for copyright info
    ==17792== Command: ./0509
    ==17792==
    ==17792== Conditional jump or move depends on uninitialised value(s)
    ==17792==    at 0x4008B8: main (0509test.cpp:9)
    ==17792==
    sum is not 33
    ==17792==
    ==17792== HEAP SUMMARY:
    ==17792==     in use at exit: 0 bytes in 0 blocks
    ==17792==   total heap usage: 0 allocs, 0 frees, 0 bytes allocated
    ==17792==
    ==17792== All heap blocks were freed -- no leaks are possible
    ==17792==
    ==17792== Use --track-origins=yes to see where uninitialised values come from
    ==17792== For lists of detected and suppressed errors, rerun with: -s
    ==17792== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)

**五 分析**

==17792== Conditional jump or move depends on uninitialised value(s)
    ==17792==    at 0x4008B8: main (0509test.cpp:9)

程序的第9行，程序的跳转依赖于一个未初始化的变量a\[2\].Valgrind准确地发现了上述程序中存在的错误。