關於C++數組的大小使用變量

參考：

1. https://www.py4u.net/discuss/108969

2. https://juejin.cn/post/6931366725602508807

 

在一次代碼中看到代碼里面數組大小用變量，竟然在g++下編譯通過，書本上不是說C++ 的數組大小不能用變量的嗎，一定要是確定大小

代碼如下：

int main() {
        int n;
        std::cin>>n;
        int a[n];
        return 0;
}

g++ -g main.cpp 並沒有報錯

 

收集到資料如下：

1. C99 支持變化長度數組，但是C++不支持，使用visual studio微軟編譯器，確實編譯報錯，說明C++標准不支持變化長度數組

In the C99 version of the C standard, variable length arrays are permitted. However, they are not permitted in any version of C++; you're seeing a G++ extension. 、
Note that Microsoft's C compiler does not fully support C99; since G++ supports C99 it's easy enough to apply the VLA support to C++ as an extension.

 

C99如何支持變化長度數組見 參考2

2. g++的擴展功能，默認支持vla

These are called variable length arrays (VLA) and are a g++ compiler extension which is not part of the C++ standard. Do not use it in C++ if you want your code to be portable.

You can make g++ emit a warning with the -Wvla compilation flag, or an error with flag -Werror=vla. I usually compile with -pedantic-errors, which catches this and many other deviations from the standard.

使用g++ -g -Werror=vla main.cpp 編譯確實報錯