函数代码：

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QDebug>
#include <stdlib.h>
#define cout qDebug()
#include <QFileDialog>
#include <QTextCodec>

//定义一个枚举类型
enum MyCode
{
    utf_8, gbk
};

QString path = "";

enum MyCode flag;

QTextCodec *co;

void MainWindow::test() //类中声明，类外定义，并且定义是需要加上作用域。
{
    flag = utf_8;
    //QLable的操作'
    //给标签设置内容
    ui->label->setText("hello qt");

    //获取标签的内容，返回值为QString
    QString str = ui->label->text();
    cout << "str = " << str;

    //QTextEdit操作
    ui->textEdit->setText("hello Mike");
    str = ui->textEdit->toPlainText();
    cout << "str = " << str;
}

//构造函数，主要做初始化操作
MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    //QLable的操作'
    //给标签设置内容
    //ui->label->setText("hello qt");

    //test();

    //给标签设置内容：
    //ui->label->setText("你好！欢迎来到程序的世界");

    //要想实现中文，必须为utf-8编码
    co = QTextCodec::codecForName("GBK");

    //co->fromUnicode(); //把UTF-8转化为GBK
    //co->toUnicode(); //把一个GBK编码的字符串转化成 UTF-8

    //const char *str = "你好！欢迎来到程序的世界";
    //ui->label->setText(co->toUnicode(str));

    ui->textEdit->setText(co->toUnicode("嗨！ Mike，让我们开始吧！"));
}

//析构函数，主要做清理操作（对象关闭前）
MainWindow::~MainWindow()
{
    delete ui;
}

//打开按钮的处理函数
void MainWindow::on_actionopen_triggered()
{
    //1. 打开一个文件，获取文件的路径
    path = QFileDialog::getOpenFileName();
    //cout << "path = "<<path;
    if(path == "") //没有选择路径
    if(path.isEmpty())
    {
        return;
    }

    //cout << "11111111111111";

    //2. 通过Qt控件获取路径，此路径是utf-8编码，需要转换成gbk编码
    //同时将Qstring类型转换为char *
    char *fileName = co->fromUnicode(path).data();
    //cout << "filename = " << fileName;

    //3. 打开文件,fopen()，fopen()如果有中文，需要gbk
    FILE *fp = fopen(fileName, "rb");
    if(NULL == fp)
    {
         cout << "on_actionopen_triggered fopen error";
         return;
    }

    //4. 循环读文件类型fgets()， 读取的类型是char *
    char buf[1024];
    QString str = "";
    while(!feof(fp))
    {
        memset(buf, 0,  sizeof(buf));
        fgets(buf, sizeof(buf), fp);
        if(flag == utf_8)
            str = str + buf;
        else if(flag == gbk)
        {
            str = str + co->toUnicode(buf);
        }
    }

    //5. 把读取的内容给编辑区setText()
    ui->textEdit->setText(str);
    //6.关闭文件
    fclose(fp);
}

void MainWindow::on_actionUTF_8_triggered()
{
    //按下此按钮选择utf-8编码
    flag = utf_8;
    ui->label->setText(co->toUnicode("当前以utf-8编码显式"));
}

void MainWindow::on_actionGBK_triggered()
{
    flag = gbk;
    ui->label->setText("gbk");
    ui->label->setText(co->toUnicode("当前以gbk编码显式"));
}
//另存为 按钮的函数槽
void MainWindow::on_actionsaveas_triggered()
{
    //1. 获取路径
    path = QFileDialog::getSaveFileName();
    if("" == path)
    {

        return;
    }

    //2. 将路径转换为gbk类型
    char *fileName = co->fromUnicode(path).data();

    //3. 打开文件，fopen(),有中文需要gbk
    FILE *fp = fopen(fileName, "wb");
    if(NULL == fp)
    {
        cout << "on_actionsaveas_triggered fopen err";
        return;
    }

    //4. 获取编辑区的内容（Qstring类型）
    QString str = ui->textEdit->toPlainText();

    //5. 将编辑区的内容QString转换为char *
    const char *buf = str.toStdString().data();

    //6. 将编辑区的文件写入文件 fputs
    fputs(buf, fp);

    //7. 关闭文件
    fclose(fp);
}
//撤销按钮
void MainWindow::on_actionundo_triggered()
{
    ui->textEdit->undo();
}

//复制按钮
void MainWindow::on_actioncpy_triggered()
{
    ui->textEdit->copy();
}

//粘贴按钮
void MainWindow::on_actionpaste_triggered()
{
    ui->textEdit->paste();
}

//剪切按钮
void MainWindow::on_actioncut_triggered()
{
    ui->textEdit->cut();
}

//编译按钮
void MainWindow::on_actioncompile_triggered()
{
    if(path.isEmpty())
        return;

    //cout << "path = " << path;

    QString demo = path;
    demo.replace(".c", ""); //将.c替换为空字符
    //cout << "demo = " << demo;

    QString cmd = QString("gcc %1 -o %2").arg(path).arg(demo);

    cout << "cmd = "<<cmd;

    //如果有中文，需要转化gbk，同时将QString 转换为 char *;
    int ret = system(co->fromUnicode(cmd).data());
    //cout << "ret = " << ret;
    if(ret != 0)
    {
        cmd = QString("cmd /k gcc %1 -o %2").arg(path).arg(demo);
        system(co->fromUnicode(cmd).data());
        return;
    }
    cmd = QString("cmd /k %1").arg(demo);
    system(co->fromUnicode(cmd).data());
}

void MainWindow::on_actionexit_triggered()
{
    exit(0);
}

void MainWindow::on_actionsave_triggered()
{
    if(path.isEmpty())
    {
        //1.获取路径
        path = QFileDialog::getSaveFileName();
     }

    //2. 将路径转换为gbk类型
    char *fileName = co->fromUnicode(path).data();

    //3. 打开文件，fopen(),有中文需要gbk
    FILE *fp = fopen(fileName, "wb");
    if(NULL == fp)
    {
        cout << "on_actionsave_triggered fopen err";
        return;
    }

    //4. 获取编辑区的内容（Qstring类型）
    QString str = ui->textEdit->toPlainText();

    //5. 将编辑区的内容QString转换为char *
    const char *buf = str.toStdString().data();

    //6. 将编辑区的文件写入文件 fputs
    fputs(buf, fp);

    //7. 关闭文件
    fclose(fp);
}

void MainWindow::on_actionnew_triggered()
{
    //编辑区清空
    //ui->textEdit->setText("");
    ui->textEdit->clear();
    //路径情况

    //path = "";
    path.clear();
}