QT use of undeclared identifier 'cout'

在QT 5.12中直接使用cout将提示错误如下：

添加库 #include<iostream>，并将cout&end改为std::cout&std::endl

代码如下：

 #include "mainwindow.h"
 #include<iostream>
 #include <QApplication>

 int main(int argc, char *argv[])
 {
     QApplication a(argc, argv);
     MainWindow w;
     w.show();

     std::cout <<"hello world" << std::endl;

     return a.exec();
 }

此时错误警告消失，但是仍无窗口输出；

在qt的工程文件(.pro文件)中加入以下代码：

CONFIG += console

代码如下：

 #-------------------------------------------------
 #
 # Project created by QtCreator --05T16::
 #
 #-------------------------------------------------

 QT       += core gui

 greaterThan(QT_MAJOR_VERSION, ): QT += widgets

 TARGET = VCICAN
 TEMPLATE = app

 # The following define makes your compiler emit warnings if you use
 # any feature of Qt which has been marked as deprecated (the exact warnings
 # depend on your compiler). Please consult the documentation of the
 # deprecated API in order to know how to port your code away from it.
 DEFINES += QT_DEPRECATED_WARNINGS

 # You can also make your code fail to compile if you use deprecated APIs.
 # In order to do so, uncomment the following line.
 # You can also select to disable deprecated APIs only up to a certain version of Qt.
 #DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000    # disables all the APIs deprecated before Qt 6.0.

 CONFIG += c++
 CONFIG += console

 SOURCES += \
         main.cpp \
         mainwindow.cpp

 HEADERS += \
         mainwindow.h

 FORMS += \
         mainwindow.ui

 # Default rules for deployment.
 qnx: target.path = /tmp/$${TARGET}/bin
 else: unix:!android: target.path = /opt/$${TARGET}/bin
 !isEmpty(target.path): INSTALLS += target

 DISTFILES +=

此时cout函数可正常运行

参考：

https://blog.csdn.net/u014563989/article/details/44537727

https://zhidao.baidu.com/question/143715512.html

http://blog.sina.com.cn/s/blog_4f183d960100sdxf.html

http://www.qtcn.org/bbs/simple/?t21816.html