c++ - vector 构造函数标识为函数

Question

这个问题已经有答案了:

A confusing detail about the Most Vexing Parse (4 个回答)

已关闭 1 年前。

考虑这段代码:

#include <iostream>
#include <sstream>
#include <iterator>
#include <vector>
#include <string>
    
int main() {
    std::istringstream ss("abcabc abc a b e");
    std::vector<std::string> words(std::istream_iterator<std::string>(ss), std::istream_iterator<std::string>());
    std::string deciphered;
    int shift = 5;
    for (size_t i = 0; i < shift; i++)
    {
        for (size_t j = 0; i + j < words.size(); j += shift)
        {
            deciphered += words[i + j];
        }
    }
}

基本上，我想拆分单词并将它们存储到我的 words 中大批。但我遇到编译错误:

main.cpp: In function 'int main()':
main.cpp:14:40: error: request for member 'size' in 'words', which is of non-class type 'std::vector<std::__cxx11::basic_string<char> >(std::istream_iterator<std::__cxx11::basic_string<char> >, std::istream_iterator<std::__cxx11::basic_string<char> > (*)())'
   14 |       for (size_t j = 0; i + j < words.size(); j += shift)
      |                                        ^~~~
main.cpp:16:33: warning: pointer to a function used in arithmetic [-Wpointer-arith]
   16 |        deciphered += words[i + j];
      |                                 ^
main.cpp:16:33: error: invalid conversion from 'std::vector<std::__cxx11::basic_string<char> > (*)(std::istream_iterator<std::__cxx11::basic_string<char> >, std::istream_iterator<std::__cxx11::basic_string<char> > (*)())' to 'char' [-fpermissive]
   16 |        deciphered += words[i + j];
      |                      ~~~~~~~~~~~^
      |                                 |
      |                                 std::vector<std::__cxx11::basic_string<char> > (*)(std::istream_iterator<std::__cxx11::basic_string<char> >, std::istream_iterator<std::__cxx11::basic_string<char> > (*)())
In file included from c:\mingw\lib\gcc\mingw32\9.2.0\include\c++\string:55,
                 from c:\mingw\lib\gcc\mingw32\9.2.0\include\c++\bits\locale_classes.h:40,
                 from c:\mingw\lib\gcc\mingw32\9.2.0\include\c++\bits\ios_base.h:41,
                 from c:\mingw\lib\gcc\mingw32\9.2.0\include\c++\ios:42,
                 from c:\mingw\lib\gcc\mingw32\9.2.0\include\c++\ostream:38,
                 from c:\mingw\lib\gcc\mingw32\9.2.0\include\c++\iostream:39,
                 from main.cpp:1:
c:\mingw\lib\gcc\mingw32\9.2.0\include\c++\bits\basic_string.h:1186:25: note:   initializing argument 1 of 'std::__cxx11::basic_string<_CharT, _Traits, _Alloc>& std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::operator+=(_CharT) [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]'
 1186 |       operator+=(_CharT __c)
      |                  ~~~~~~~^~~

从错误来看，我的变量 words被识别为一个函数。

我很困惑，这种行为的原因是什么？我该如何解决它？

Answer 1

这就是所谓的 most vexing parse ，在这种情况下，您应该使用大括号初始化语法，这将使编译器知道您正在尝试构造类的实例而不是声明函数。

即std::vector<int> a{}而不是std::vector<int> a()