`在C ++中没有命名类型错误 [英] `does not name a type` error in C++

问题描述

我不知道要搜索什么来找到这个的解释，所以我问。

我有这个代码，报告错误：

  struct设置{
 int width; 
 int height; 
}设置; 
 
 settings.width = 800; //'settings'没有命名类型错误
 settings.height = 600; //'settings'没有指定类型错误
 
 int main（）{
 cout< settings.width<< < settings.height< endl; 
  

但是如果我在main中赋值，它的工作原理：

  struct设置{
 int width; 
 int height; 
}设置; 
 
 main（）{
 settings.width = 800; //没有错误
 settings.height = 600; //没有错误
  

你能解释一下为什么吗？

EDIT：

关于Ralph Tandetzky的回答，这里是我的完整结构代码。

 结构设置{
 struct Dimensions可以显示如何为我的代码段结构分配值{
 int width; 
 int height; 
} screen; 
 
 struct Build_menu：Dimensions {
 int border_width; 
} build_menu; 
}设置; 
  

解决方案

C ++。如果你对有时看到 = 符号在函数上下文之外使用的事实感到困惑，例如：

  int x = 42; //< ==这不是分配！ 
 
 int main（）
 {
 // ... 
} 
  

这是因为 = 符号也可以用于初始化。在您的示例中，您不是初始化数据成员 width 和 height ，您正在为它们分配一个值。 / p>

I don't know what to search to find an explanation for this, so I am asking.
I have this code which reports error:

struct Settings{
    int width;
    int height;
} settings;

settings.width = 800; // 'settings' does not name a type error
settings.height = 600; // 'settings' does not name a type error

int main(){
    cout << settings.width << " " << settings.height << endl;

but if I put the value assignment in main, it works:

struct Settings{
    int width;
    int height;
} settings;

main () {
    settings.width = 800; // no error
    settings.height = 600; // no error

Can you explain me why?

EDIT:
Regarding to Ralph Tandetzky's answer, here is my full struct code. Could you show me how to assign the values as you did with my snippet struct?

struct Settings{
    struct Dimensions{
        int width;
        int height;
    } screen;

    struct Build_menu:Dimensions{
        int border_width;
    } build_menu;
} settings;

解决方案

You cannot put assignments outside the context of a function in C++. If you're puzzled by the fact that you sometimes saw the = symbol being used outside the context of a function, such as:

int x = 42; // <== THIS IS NOT AN ASSIGNMENT!

int main()
{
    // ...
}

That's because the = symbol can be used for initialization as well. In your example, you are not initializing the data members width and height, you are assigning a value to them.

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