C ++模板编译错误：'>'令牌之前的预期主表达式 [英] C++ template compilation error: expected primary-expression before ‘>’ token

问题描述

此代码按预期编译和工作（它在运行时抛出，但不介意）：

This code compiles and works as expected (it throws at runtime, but never mind):

#include <iostream>
#include <boost/property_tree/ptree.hpp>

void foo(boost::property_tree::ptree &pt) 
{
    std::cout << pt.get<std::string>("path"); // <---
}

int main()
{
    boost::property_tree::ptree pt;
    foo(pt);
    return 0;
}

但是一旦我添加模板并更改 foo 原型到

But as soon as I add templates and change the foo prototype into

template<class ptree>
void foo(ptree &pt)

我在GCC中遇到错误： p>

I get an error in GCC:

test_ptree.cpp: In function ‘void foo(ptree&)’:
test_ptree.cpp:7: error: expected primary-expression before ‘>’ token

但没有MSVC ++的错误！错误在标记行< --- 中。再次，如果我把问题行改成

but no errors with MSVC++! The error is in the marked line <---. And again, if I change the problem line into

--- std::cout << pt.get<std::string>("path"); // <---
+++ std::cout << pt.get("path", "default value");

错误消失（问题在于显式< std :: string> ; ）。

the error disappears (the problem is in explicit <std::string>).

Boost.PropertyTree 要求Boost> = 1.41。请帮助我理解并修复此错误。

Boost.PropertyTree requires Boost >= 1.41. Please help me to understand and fix this error.

请参阅模板：模板函数不能很好地与类的模板成员函数

See Templates: template function not playing well with class’s template member function — a similar popular question containing other good answers and explanations.

推荐答案

您需要执行以下操作：

std::cout << pt.template get<std::string>("path");

使用模板

（也就是说，由于 pt：code> typename ：get 是模板成员对模板参数的依赖，你需要告诉编译器它是一个模板。）

(That is, since pt::get is a template member dependent on a template parameter, you need to tell the compiler it's a template.)

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