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 2019-09-05T16:30:11
#
#-------------------------------------------------

QT       += core gui

greaterThan(QT_MAJOR_VERSION, 4): 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 6.0.0

CONFIG += c++11
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