Solution to error: ‘_1’ was not declared in this scope under C++11 standard

最新推荐文章于 2023-08-20 00:31:59 发布

jimodeyangguang

最新推荐文章于 2023-08-20 00:31:59 发布

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分类专栏： C++ 文章标签： C++11

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本文介绍了一种在C++编程中遇到的编译错误“_1未在该范围内声明”的解决方案。通过将标准库的占位符正确地置于std::placeholders命名空间下，解决了bind函数中的参数引用问题。

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The problem is when I compiled the following program, the compiler showed me an error like this " error: ‘_1’ was not declared in this scope".

1 #include <iostream>
2 #include <vector>
3 #include <functional>
4 #include <string>
5 #include <algorithm>
6
7 using namespace std;
8
9 bool check_size(const string &s, string::size_type sz) {
10 cout << s << endl;
11 return s.size() >= sz;
12 }
13
14 auto newCallable = bind(check_size, _1, 6);
15
16 int main() {
17
18 string s = "Hello World !!!";
19 newCallable(s);
20 return EXIT_SUCCESS;
21 }

I guess the problem should be caused by lack of some important header file which I didn't found.

Finally, I found the solution to this error: the _1 form of placeholder should be in namespace std::placeholders. So I corrected my program in line 16

as follows:

auto newCallable = bind(check_size, placeholders::_1, 6);

Then it works well.