没有从'value_type'(aka'char')到'string'(aka'basic_string< char，char_traits< char&gt ;,分配器< char>')的可行转换

问题描述

string convert(string name)
{
  string code = name[0];
  ...
}

我从这行得到从'value_type'(aka'char')到'string'(aka'basic_string，allocator>')的不可行转换".

I get "no viable conversion from 'value_type' (aka 'char') to 'string' (aka 'basic_string, allocator >')" from this line.

如果我将其更改为:

string convert(string name)
{
  string code;
  code = name[0];
  ...
}

然后它起作用.谁能解释为什么?

Then it works.Can anyone explain why?

推荐答案

类std :: string(相应地std :: basic_string)具有赋值运算符

Class std::string (correspondingly std::basic_string) has assignment operator

basic_string& operator=(charT c);

，此代码段中使用了该赋值运算符

and this assignment operator is used in this code snippet

string convert(string name)
{
  string code;
  code = name[0]; // using of the assignment operator
  ...
}

但是该类没有合适的构造函数，您可以编写

However the class does not has an appropriate constructor that you could write

string code = name[0];

您可以这样写

string code = { 1, name[0] };

或喜欢

string code( 1, name[0] );

使用构造函数

basic_string(size_type n, charT c, const Allocator& a = Allocator());

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