与未指定行为的字符串字面结果进行比较？ [英] Comparison with string literal results in unspecified behaviour?
问题描述
我在尝试编写程式时遇到问题。它只是一个Windows控制台程序，我是非常新的C ++。这只是我的第四个程序。
我遇到的问题是，当我运行我的程序，我没有错误，但很多警告说，与字符串字面值结果
当程序运行，而不是添加数字，我想要它只是给我一个随机的大数字
以下是代码：
#include< iostream>
using namespace std;
int main（）
{
int hold;
int i;
int n;
i = 6;
int result;
int * price;
char items [100] [100];
if（items == 0）
cout<< 没有项目可以存储;
else
{
for（n = 0; n
cout< Item＃<< n<< ：;
cin>>项目[n];
}
cout<< \\\
You Entered：\\\
;
for（n = 0; n< i; n ++）
cout<项目[n] ，;
}
for（n = 0; n< i; n ++）
{
if（items [n] ==ab）{
price [n] = 2650;
}
else if（items [n] ==ae）{
price [n] = 1925;
}
else if（items [n] ==ie）{
price [n] = 3850;
}
else if（items [n] ==bt）{
price [n] = 3000;
}
else if（items [n] ==pd）{
price [n] = 2850;
}
else if（items [n] ==ga）{
price [n] = 2600;
}
}
for（n = 0; n
result = result + price [n ];
}
cout<< \\\
Total gold for this build：<<结果;
cin>>>保持;
return 0;
}
任何帮助。有可能是大的，我做错了。 if语句中的名称都是当前的占位符，我将添加更多的if语句，当我可以得到它与裸6，这是它需要工作。
char [100] 和字符串文字只会将它们作为2 char * 或更好地称为2个指针，指针不能等于 items [n] ==ae永远不能为true，而不是这样，你应该使用 std :: string 以保存字符串为： std :: string items [100]
//初始化项目
if（items [n] ==ae）...
b $ b
或者你应该使用 strcmp 来比较字符串，但是remeber strcmp 因此您的代码将为：
char items [100] [100];
//初始化项目
if（strcmp（items [n]，ae）== 0）...
另外一个注意事项是 if（items == 0）没有用，因为 items 在堆栈上分配，而不是在堆中！
I am having a problem with the program I am trying to code. It's just a Windows console program and I am very new to C++. It's only my 4th program.
The problem I am having is that when I run my program I have no errors but a lot of warnings that say "comparison with string literal results in unspecified behaviour" in the lines that I will highlight below.
When the program runs instead of adding the numbers I want it to it just gives me a random huge number no matter what I put in for my inputs.
Here is the code:
#include <iostream>
using namespace std;
int main()
{
int hold;
int i;
int n;
i = 6;
int result;
int * price;
char items[100][100];
if (items == 0)
cout << "No items can be stored";
else
{
for (n=0; n<i; n++)
{
cout << "Item#" << n << ": ";
cin >> items[n];
}
cout << "\nYou Entered: \n";
for (n=0; n<i; n++)
cout << items[n] << ", ";
}
for (n=0; n<i; n++)
{
if (items[n] == "ab"){
price[n] = 2650;
}
else if (items[n] == "ae"){
price[n] = 1925;
}
else if (items[n] == "ie"){
price[n] = 3850;
}
else if (items[n] == "bt"){
price[n] = 3000;
}
else if (items[n] == "pd"){
price[n] = 2850;
}
else if (items[n] == "ga"){
price[n] = 2600;
}
}
for (n=0; n<i; n++)
{
result = result + price[n];
}
cout << "\nTotal gold for this build: " << result;
cin >> hold;
return 0;
}
Any help is appreciated. There is probably something big that I've done wrong. The names in the if statements are all currently placeholders and I'll be adding a lot more if statements when I can get it to work with the bare 6 which is what it needs to work.
In C++ == only implemented internally for primitive types and array is not a primitive type, so comparing char[100] and string literal will only compare them as 2 char* or better to say as 2 pointers and since this 2 pointers can't be equal then items[n] == "ae" can never be true, instead of this you should either use std::string to hold string as:
std::string items[100];
// initialize items
if( items[n] == "ae" ) ...
or you should use strcmp to compare strings, but remeber strcmp return 0 for equal strings, so your code will be as:
char items[100][100];
// initialize items
if( strcmp(items[n], "ae") == 0 ) ...
And one extra note is if (items == 0) is useless, since items allocated on stack and not in the heap!
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