关于模板函数 返回值有点问题，费解

[ftkghost]

请各位看看，如果你全都输入负数就会发现问题了。
是因为模板中为Type分配的大小有关？

#include<iostream>
template<class Type>
bool input(Type& inp);

int main()
{
int a1;
double a2;
float a3;

if(input(a1))
std::cout<<a1<<std::endl;
else
std::cout<<"负数:"<<a1<<std::endl;

if(input(a2))
std::cout<<a2<<std::endl;
else
std::cout<<"负数:"<<a2<<std::endl;

if(input(a3))
std::cout<<a3<<std::endl;
else
std::cout<<"负数:"<<a3<<std::endl;

system("Pause");
return 0;
}

template<class Type>
bool input(Type& inp)
{
Type in;
int i=3;
do{
std::cout<<"请输入一个非负数:";
std::cin>>in;
if(in<0){
std::cout<<"输入错误，您还有"<<(i-1)<<"次机会!"<<std::endl;
i--;
continue;
}
else{
inp=in;
return true;
}
}while(i>0);
return false;
}

[Leaveye]

在模板函数内，返回假之前，加一句赋值
inp = in;

另外还有一处BUG，如果输入的不是数字或小数点，那么到程序结束也不会再等待输入了。

[Leaveye]

重置 cin ，这里有段代码，你可以参考一下：
It would be better to prompt again for a correct value. There are two complications to consider in order in doing this. First, once cin gets into an error state, it needs to be reset before reuse. This is done with the istream member function clear. Second, when an input operation fails the bad data is still left in the input stream. The next read will get the value of "A" again. The istream member function ignore can be used to remove this bad data from the input stream.

#include <iostream>
using namespace std;

int main()
{
int age;

cout << "Enter you age: ";
cin >> age;

while (!cin)
{
cin.clear();
//reset cin, so more input can be done
cin.ignore(100,'\n');
//remove bad data, up to 100 characters
//or until the end of line is reached
cout << "Please enter a number for you age: ";
cin >> age;
}
if (age > 21)
{
cout << "You're legal at " << age < }
else
{
cout << "Sorry kid, you're only " << age << endl;
}

return 0;

}

Here's the results from this version.

Enter you age: A
Please enter a number for you age: s
Please enter a number for you age: t
Please enter a number for you age: u
Please enter a number for you age: p
Please enter a number for you age: i
Please enter a number for you age: d
Please enter a number for you age: u
Please enter a number for you age: s
Please enter a number for you age: e
Please enter a number for you age: r
Please enter a number for you age: 23
You're legal at 23

Generally, it is better to anticipate and check for user error on input than to risk program failure or errors.

摘自：http://cplus.about.com/library/weekly/aa030702b.htm

[zxl_llx]

我知道了：应当：
template<class Type>
bool input(Type& inp)
{
Type in;
int i=3;
do{
std::cout<<"请输入一个非负数:";
std::cin>>in;
if(in<0){
std::cout<<"输入错误，您还有"<<(i-1)<<"次机会!"<<std::endl;
i--;
inp=in;//<-------------加上这一句，就可以了。
continue;
}
else{
inp=in;
return true;
}
}while(i>0);
return false;
}

[ftkghost]

谢谢

[ftkghost]

hehe 不好意思 低级错误

a1,a2,a3没有初值

谢谢啊

[ftkghost]

Leaveye(~枝)(完全了解系统，也要实际量测性能)

另外还有一处BUG，如果输入的不是数字或小数点，那么到程序结束也不会再等待输入了。

请问这个BUG怎么改？以前也遇到过
难道要加个if语句限制输入只能是数字和小数点？

[ftkghost]

顶一下