問題描述

我剛遇到這個問題

error: request for member ‘show’ in ‘myWindow’, which is of non-class type ‘MainGUIWindow()’

嘗試編譯一個簡單的 qt 應用程序時:

when trying to compile a simple qt-application:

#include <QApplication>
#include "gui/MainGUIWindow.h"


int main( int argc, char** argv )
{
  QApplication app( argc, argv );


  MainGUIWindow myWindow();
  myWindow.show();


  return app.exec();
}

我通過替換

MainGUIWindow myWindow(); 

由

MainGUIWindow myWindow;

但我不明白其中的區別.我的問題:有什么區別?

but I don't understand the difference. My question: What is the difference?

問候，德克

推薦答案

其他答案正確地指出括號版本實際上是一個函數聲明.為了直觀地理解它，假設你寫的 MainGUIWindow f(); 看起來更像一個函數，不是嗎?:)更有趣的問題是

The other answers correctly state that the parentheses version is actually a function declaration. To understand it intuitively, suppose you wrote MainGUIWindow f(); Looks more like a function, doesn't it? :) The more interesting question is what is the difference between

MainGUIWindow* p = new MainGUIWindow;

和

MainGUIWindow* p = new MainGUIWindow();

帶括號的版本稱為值初始化，而沒有括號的版本稱為默認初始化.對于非 POD 類，兩者沒有區別.然而，對于 POD 結構，值初始化涉及將所有成員設置為 0，

The version with parentheses is called value-initialization, whereas the version without is called default-initialization. For non-POD classes there is no difference between the two. For POD-structs, however, value-initialization involves setting all members to 0,

my2c

補充:一般來說，如果某個句法結構既可以解釋為聲明又可以解釋為其他東西，編譯器總是會以聲明的方式解決歧義.

Addition: In general, if some syntactic construct can be interpreted both as a declaration and something else, the compiler always resolves the ambiguity in favor of the declaration.

這篇關于使用 () 或不使用 () 創建對象的區別的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網！