C++ 编译错误(gcc 4.7)

Question

我正在尝试在第 5.9 章 Bjarne Stroustrup The C++ Programming Language 的末尾做 11 个练习。

  1 #include <iostream>
  2 #include <string>
  3 #include <vector>
  4 #include <algorithm>
  5 
  6 void print(std::vector<std::string>::const_iterator str) {
  7    std::cout << *str;
  8 }
  9 
 10 int main(void) {
 11    std::vector<std::string> words;
 12    std::string tmp;
 13 
 14    std::cin >> tmp;
 15    while (tmp != "Quit") {
 16       words.push_back(tmp);
 17       std::cin >> tmp;
 18    }
 19 
 20    for_each(words.begin(), words.end(), print);
 21 
 22    return 0;
 23 }

当我取消注释第 20 行时，出现此错误:

In file included from /usr/include/c++/4.7/algorithm:63:0,
                 from 5.9.11.cpp:4:
/usr/include/c++/4.7/bits/stl_algo.h: In instantiation of ‘_Funct std::for_each(_IIter, _IIter, _Funct) [with _IIter = __gnu_cxx::__normal_iterator<std::basic_string<char>*, std::vector<std::basic_string<char> > >; _Funct = void (*)(__gnu_cxx::__normal_iterator<const std::basic_string<char>*, std::vector<std::basic_string<char> > >)]’:
5.9.11.cpp:20:44:   required from here
/usr/include/c++/4.7/bits/stl_algo.h:4442:2: error: could not convert ‘__first.__gnu_cxx::__normal_iterator<_Iterator, _Container>::operator*<std::basic_string<char>*, std::vector<std::basic_string<char> > >()’ from ‘std::basic_string<char>’ to ‘__gnu_cxx::__normal_iterator<const std::basic_string<char>*, std::vector<std::basic_string<char> > >’

编译命令:

g++ prog.cpp -o prog -Wall

我做错了什么？

Answer 1

回调函数应该采用 std::string，而不是迭代器。 for_each 传递每个元素本身。因此，您的函数将变为:

void print(const std::sting &str) {
    std::cout << str << ' '; //note I separated the words
}

有关固定示例(包括 for_each 上的 std::，以及其他一些小差异)，请参阅 this run .

在 C++11 中(您的编译器可以通过 -std=c++0x 或 -std=c++11 访问)，您甚至不必担心关于 std::for_each 循环遍历容器，因为 C++11 引入了 ranged-for 循环:

for (const std::string &str : words)
    std::cout << str << ' ';