ISO C++ 不允许使用变长数组，g++ 很高兴地告诉你，如果你增加通过向它传递 -pedantic 标志来严格它.

ISO C++ disallows the use of variable length arrays, which g++ happily tells you if you increase the strictness of it by passing it the -pedantic flag.

使用 -pedantic 将发出有关违反标准的警告.如果您希望 g++ 发出错误并因此拒绝编译；使用 -pedantic-errors.

Using -pedantic will issue a warning about things breaking the standard. If you want g++ to issue an error and with this refuse compilation because of such things; use -pedantic-errors.

g++ -Wall -pedantic -std=c++11 apa.cpp

apa.cpp: In function ‘int main(int, char**)’:
apa.cpp:8:13: warning: ISO C++ forbids variable length array ‘ints’ [-Wvla]
   int ints[a];
             ^
apa.cpp:8:7: warning: unused variable ‘ints’ [-Wunused-variable]
   int ints[a];
       ^