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(yīng)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(qū)別.我的問題:有什么區(qū)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(shù)聲明.為了直觀地理解它，假設(shè)你寫的 MainGUIWindow f(); 看起來更像一個函數(shù)，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(qū)別.然而，對于 POD 結(jié)構(gòu)，值初始化涉及將所有成員設(shè)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(jié)構(gòu)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(guān)于使用 () 或不使用 () 創(chuàng)建對象的區(qū)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(wǎng)！