没有从“value_type"(又名“char")到“string"(又名“basic_string<char, char_traits<char>, allocator<char>&gt;')的可行转换

no viable conversion from #39;value_type#39; (aka #39;char#39;) to #39;string#39; (aka #39;basic_stringlt;char, char_traitslt;chargt;, allocatorlt;chargt; gt;#39;)(没有从“value_type(又名“char)到“string(又名“basic_stringchar, char_traitschar, allocatorchargt;)的可行转

问题描述

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

我从这一行得到从'value_type'(又名'char')到'string'(又名'basic_string，分配器>')没有可行的转换".

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];
  ...
}

然后就可以了.谁能解释一下为什么?

Then it works. Can anyone explain why?

推荐答案

类std::string(对应std::basic_string)有赋值运算符

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

basic_string& operator=(charT c);

并且此代码片段中使用了此赋值运算符

and this assignment operator is used in this code snippet

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

但是该类没有您可以编写的适当构造函数

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

string code = name[0];

你可以这样写

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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