编译器无法识别模板函数中的映射迭代器

2022-01-10 00:00:00 iterator templates c++ map

我有以下代码.

template<class key,class val>
bool has_key(key chkey,std::map<key,val> map){
  for (std::map<key,val>::iterator it = map.begin(); #line 13 referenced by gcc
      it!=map.end(); ++it){
    if(chkey == it->first) return true;
  }
  return false;
}

GCC 给我以下错误.

GCC is giving me the following error.

objects.hpp: In function `bool has_key(key, std::map<key, val, std::less<_Key>,
  std::allocator<std::pair<const _Key, _Tp> > >)':
objects.hpp:13: error: expected `;' before "it"
objects.hpp:14: error: `it' was not declared in this scope

不知何故，它"没有被初始化，Sam Hain 是怎么回事?！

Somehow "it" is not being initialized, what in Sam Hain is going on here?!

推荐答案

你需要 typename 关键字:

for (typename std::map<key,val>::iterator it = map.begin(); #line 13 referenced by gcc
  it!=map.end(); ++it){

另请参阅:为什么我们在这里需要 typename?

这是因为您在模板定义中，而 iterator 是一个依赖名称.以前有人问过这个问题.

This is because you are in a template definition and iterator is a dependent name. This has been asked before.

g++不是类型"错误

C++ 模板:'不是从类型派生的'

模板中依赖类型的问题

相关文章