从临时流中提取字符时 GCC 编译器错误
我正在尝试从流中读取单个字符。使用以下代码，我收到“不明确的重载”编译器错误（GCC 4.3.2、和 4.3.4）。我做错了什么？
#include <iostream>
#include <sstream>
int main()
{
char c;
std::istringstream("a") >> c;
return 0;
}
备注：
- Visual Studio 2008 编译没有错误
- 其他类型（
int、double）可以工作 - 如果我首先创建一个变量
std::istringstream iss("a") ;国际空间站>> c，编译器没有报错
I'm trying to read a single character from a stream. With the following code I get a "ambiguous overload" compiler error (GCC 4.3.2, and 4.3.4). What I'm doing wrong?
#include <iostream>
#include <sstream>
int main()
{
char c;
std::istringstream("a") >> c;
return 0;
}
Remarks:
- Visual Studio 2008 compiles without errors
- Other types (
int,double) are working - If I first create a variable
std::istringstream iss("a"); iss >> c, the compiler gives no error
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字符的提取运算符
>>是非成员函数模板：由于它通过非
const引用获取其第一个参数，因此您不能使用临时那里有右值。因此，您的代码无法选择此重载，只能选择各种成员函数重载，其中没有一个与此用法匹配。您的代码在 C++11 中有效，因为还有一个提取运算符将右值引用作为第一个参数。
该编译器的许多非标准扩展之一是允许临时右值绑定到非
const引用。大多数基本类型的提取运算符都是成员函数，可以在临时上调用右值。
iss是一个非临时左值，因此它可以绑定到非const参考。The extraction operator
>>for characters is a non-member function template:Since this takes its first argument by non-
constreference, you can't use a temporary rvalue there. Therefore, your code cannot select this overload, only the various member function overloads, none of which match this usage.Your code is valid in C++11, because there is also an extraction operator taking an rvalue reference as the first argument.
One of that compiler's many non-standard extensions is to allow temporary rvalues to be bound to non-
constreferences.Most extraction operators for fundamental types are member functions, which can be called on a temporary rvalue.
issis a non-temporary lvalue, so it can be bound to a non-constreference.读取
char的operator>>的签名是根据语言规则，临时变量不能绑定到第一个参数，因为临时变量不能绑定到非常量参考。
Visual Studio 2008 允许将其作为 MS 扩展。以后的版本会警告你这是不允许的。
The signature for the
operator>>reading acharisAccording to the language rules, a temporary cannot bind to the first parameter as a temporary cannot bind to a non-const reference.
Visual Studio 2008 allows this as an MS extension. Later versions will warn you that it is not allowed.