为什么即使要求，gcc也不会抱怨数组边界？ [英] Why isn't gcc complaining about array bounds even if requested?

问题描述

我正在使用gcc 4.9.0，并且我希望看到编译器警告我有关超出数组范围的问题。如果我对此进行编译

I'm using gcc 4.9.0 and I would like to see compiler warn me about exceeded array bounds. If I compile this

int main()
{
    int table[5]={0};
    table[8] = 1234;
    int x = table[10];
}

with g ++ -O2 -Wall main.cpp -o main.exe仅我得到有关未使用的x的警告：

with g++ -O2 -Wall main.cpp -o main.exe I only get warning about unused x:

main.cpp: In function 'int main()':
main.cpp:8:7: warning: unused variable 'x' [-Wunused-variable]
int x = table[10];
   ^

来自gcc文档（ https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#Warning-Options ）我看到-O2与-Wall一起应启用-Warray-bounds = 1检查。如果我尝试添加-Warray-bounds，情况不会改变。实际上，编译器甚至无法识别-Warray-bounds = 1：

From gcc documentation (https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#Warning-Options) I see that -O2 together with -Wall should enable -Warray-bounds=1 check. Things don't change if I try to add -Warray-bounds. As a matter of fact, the compiler doesn't even recognize -Warray-bounds=1:

g++: error: unrecognized command line option '-Warray-bounds=1'

现在，为什么编译器不给出任何警告错误地写入/读取数组？为何编译器无法识别‘-Warray-bounds = 1’？

Now, why doesn't compiler give any warning about incorrectly writing into / reading from the array? And why doesn't the compiler recognize '-Warray-bounds=1'?

推荐答案

编译器可能对其进行了优化。尝试制作表 易失性。

Probably compiler optimizes it away. Try making table volatile.

int main()
{
    volatile int table[]={0,0};
    table[8] = 1234;
    int x = table[10];
}

产生：

prog.cc:4:12: warning: array subscript is above array bounds [-Warray-bounds]
     table[8] = 1234;
     ~~~~~~~^
prog.cc:5:21: warning: array subscript is above array bounds [-Warray-bounds]
     int x = table[10];
             ~~~~~~~~^

这里是 实时示例 。

来自 -Warray-bounds docs：

它警告数组的下标始终超出范围

It warns about subscripts to arrays that are always out of bounds

我的猜测是g ++决定在访问从未真正发生时不发出警告。

My guess is that g++ decides not to warn when the access never actually happens.

事实上，编译器甚至无法识别-Warray-bounds = 1：

As a matter of fact, the compiler doesn't even recognize -Warray-bounds=1:

g ++：错误：无法识别命令行选项'-Warray-bounds = 1'

g ++-4.9.0不支持格式为 -Warray-bounds = n ，但在 -Warray-bounds 上也可以正常工作。 g ++-5.1.0支持 -Warray-bounds = n 。

g++-4.9.0 does not support command in the format -Warray-bounds=n, but it will work just fine with -Warray-bounds. -Warray-bounds=n is supported from g++-5.1.0.

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