在同一地址的变量如何产生2个不同的值？

本文介绍了在同一地址的变量如何产生2个不同的值？的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述 限时删除！！ 请考虑这一点： #include< iostream> using namespace std; int main（void） { const int a1 = 40; const int * b1 =& a1; char * c1 =（char *）（b1）; * c1 ='A'; int * t =（int *）c1; cout<< a1 cout<< & a1<< < t return 0; } 这个输出是： 40 65 0xbfacbe8c 0xbfacbe8c 这对我来说似乎是不可能的，除非编译器正在进行优化。怎么样 ？ 解决方案这是未定义的行为，您正在修改一个常量变量，因此您不能期望结果。我们可以通过转到草稿C ++标准部分 7.1.6.1 cv-qualifiers 段落 4 ： > 甚至提供了一个示例： const int * ciq = new const int（3）; //根据需要初始化 int * iq = const_cast< int *>（ciq）; // cast required * iq = 4; // undefined：修改const对象 在未定义行为的标准定义 1.3.24 部分给出以下可能的行为： ..]允许的未定义行为的范围从完全以不可预测的结果忽略情况，在以文件化的环境特征（有或没有发出a诊断消息）的翻译或程序执行期间行为，或执行（随着诊断消息的发出）。 [...] Consider this :#include <iostream>using namespace std;int main(void){ const int a1 = 40; const int* b1 = &a1; char* c1 = (char *)(b1); *c1 = 'A'; int *t = (int*)c1; cout << a1 << " " << *t << endl; cout << &a1 << " " << t << endl; return 0;}The output for this is :40 650xbfacbe8c 0xbfacbe8cThis almost seems impossible to me unless compiler is making optimizations. How ? 解决方案 This is undefined behavior, you are modifying a const variable so you can have no expectation as to the results. We can see this by going to the draft C++ standard section 7.1.6.1 The cv-qualifiers paragraph 4 which says: [...]any attempt to modify a const object during its lifetime (3.8) results in undefined behavior.and even provides an example:const int* ciq = new const int (3); // initialized as requiredint* iq = const_cast<int*>(ciq); // cast required*iq = 4; // undefined: modifies a const objectIn the standard definition of undefined behaviour in section 1.3.24, gives the following possible behaviors: [...] Permissible undefined behavior ranges from ignoring the situation completely with unpredictable results, to behaving during translation or program execution in a documented manner characteristic of the environment (with or without the issuance of a diagnostic message), to terminating a translation or execution (with the issuance of a diagnostic message). [...] 这篇关于在同一地址的变量如何产生2个不同的值？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！ 1403页，肝出来的..