这是什么意思? int foo = foo + 4; [英] What does this mean? int foo = foo + 4;
问题描述
#include <iostream>
int main(int argc, char** args) {
int foo = foo + 4;
std::cout << foo << std::endl;
}
后续问题是,有一个编译器标志停止这种事情?我发现 - 有时工作,更好地是完全防止它。
And a follow up question, is there a compiler flag to stop this sort of thing? I found -Wall works sometimes, better would be to prevent it entirely.
My compiler:
g++ -v
Using built-in specs.
Target: i486-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 4.4.3-4ubuntu5' --with-bugurl=file:///usr/share/doc/gcc-4.4/README.Bugs --enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --enable-shared --enable-multiarch --enable-linker-build-id --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.4 --program-suffix=-4.4 --enable-nls --enable-clocale=gnu --enable-libstdcxx-debug --enable-plugin --enable-objc-gc --enable-targets=all --disable-werror --with-arch-32=i486 --with-tune=generic --enable-checking=release --build=i486-linux-gnu --host=i486-linux-gnu --target=i486-linux-gnu
Thread model: posix
gcc version 4.4.3 (Ubuntu 4.4.3-4ubuntu5)
推荐答案
没有没有可靠的方法来阻止这种事情。它是C ++和C的一个组成部分,变量的名称在其初始化器中可见。它允许你做这样的事情
No there is no guaranteed way to stop this sort of thing. It is an integral part of C++ and C that the variable's name is visible in its initializer. It allows you to do such things as
T *t = malloc(sizeof(*t));
有关C ++问题列表的问题报告,需要在简单的情况下进行诊断,但目前编译器不需要诊断你的情况。
There is an issue report on the C++ issues list to require diagnostics in simple cases, but currently compilers are not required to diagnose your case.
它在不同的上下文中也有效 < a>。
It's also valid in a different context.
编辑:澄清 - 您的代码段的行为未定义:您正在读取未初始化变量的值。编译器不需要诊断这不意味着行为被定义。
To clarify - the behavior of your snippet is undefined: You are reading the value of a not initialized variable. That compilers are not required to diagnose this does not mean that behavior is defined.
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