参考链接
显示柱状图的值

QCustomPlot下载

下载地址：https://www.qcustomplot.com/index.php/download

选择版本2.1.0 QCustomPlot.tar.gz

QCustomPlot 的使用

解压下载的文件
把qcustomplot.h和qcustomplot.cpp放到自己的项目工程（复制文件并qt 的目录树添加存在的头文件源文件）。在使用QCustomPlot类的地址包含头文件 #include "qcustomplot.h"
添加printsupport
如果Qt版本在5.0以上，需要在.pro文件中的QT变量加上printsupport：
QT += widgets printsupport
添加帮助文档
在下载的documentation文件夹下有个qcustomplot.qch文件，将它拷贝Qt的安装文档目录下（一般为qt5.9\Docs\Qt-5.9，会根据你的Qt版本号而做相应变动），然后在QtCreator ——>工具——>选项——>帮助——>文档——>添加，选择qcustomplot.qch文件，确定，以后按F1就能跳转到QCustomPlot的帮助

实例Demo

void MainWindow::setupBarChartDemo(QCustomPlot *customPlot)
{
  demoName = "Bar Chart Demo";
  // set dark background gradient:
  QLinearGradient gradient(0, 0, 0, 400);
  gradient.setColorAt(0, QColor(90, 90, 90));
  gradient.setColorAt(0.38, QColor(105, 105, 105));
  gradient.setColorAt(1, QColor(70, 70, 70));
  customPlot->setBackground(QBrush(gradient));
  
  // create empty bar chart objects:
  QCPBars *regen = new QCPBars(customPlot->xAxis, customPlot->yAxis);
  QCPBars *nuclear = new QCPBars(customPlot->xAxis, customPlot->yAxis);
  QCPBars *fossil = new QCPBars(customPlot->xAxis, customPlot->yAxis);
  regen->setAntialiased(false); // gives more crisp, pixel aligned bar borders
  nuclear->setAntialiased(false);
  fossil->setAntialiased(false);
  regen->setStackingGap(1);
  nuclear->setStackingGap(1);
  fossil->setStackingGap(1);
  // set names and colors:
  fossil->setName("Fossil fuels");
  fossil->setPen(QPen(QColor(111, 9, 176).lighter(170)));
  fossil->setBrush(QColor(111, 9, 176));
  nuclear->setName("Nuclear");
  nuclear->setPen(QPen(QColor(250, 170, 20).lighter(150)));
  nuclear->setBrush(QColor(250, 170, 20));
  regen->setName("Regenerative");
  regen->setPen(QPen(QColor(0, 168, 140).lighter(130)));
  regen->setBrush(QColor(0, 168, 140));
  // stack bars on top of each other:
  nuclear->moveAbove(fossil);
  regen->moveAbove(nuclear);
  
  // prepare x axis with country labels:
  QVector<double> ticks;
  QVector<QString> labels;
  ticks << 1 << 2 << 3 << 4 << 5 << 6 << 7;
  labels << "USA" << "Japan" << "Germany" << "France" << "UK" << "Italy" << "Canada";
  QSharedPointer<QCPAxisTickerText> textTicker(new QCPAxisTickerText);
  textTicker->addTicks(ticks, labels);
  customPlot->xAxis->setTicker(textTicker);
  customPlot->xAxis->setTickLabelRotation(60);
  customPlot->xAxis->setSubTicks(false);
  customPlot->xAxis->setTickLength(0, 4);
  customPlot->xAxis->setRange(0, 8);
  customPlot->xAxis->setBasePen(QPen(Qt::white));
  customPlot->xAxis->setTickPen(QPen(Qt::white));
  customPlot->xAxis->grid()->setVisible(true);
  customPlot->xAxis->grid()->setPen(QPen(QColor(130, 130, 130), 0, Qt::DotLine));
  customPlot->xAxis->setTickLabelColor(Qt::white);
  customPlot->xAxis->setLabelColor(Qt::white);
  
  // prepare y axis:
  customPlot->yAxis->setRange(0, 12.1);
  customPlot->yAxis->setPadding(5); // a bit more space to the left border
  customPlot->yAxis->setLabel("Power Consumption in\nKilowatts per Capita (2007)");
  customPlot->yAxis->setBasePen(QPen(Qt::white));
  customPlot->yAxis->setTickPen(QPen(Qt::white));
  customPlot->yAxis->setSubTickPen(QPen(Qt::white));
  customPlot->yAxis->grid()->setSubGridVisible(true);
  customPlot->yAxis->setTickLabelColor(Qt::white);
  customPlot->yAxis->setLabelColor(Qt::white);
  customPlot->yAxis->grid()->setPen(QPen(QColor(130, 130, 130), 0, Qt::SolidLine));
  customPlot->yAxis->grid()->setSubGridPen(QPen(QColor(130, 130, 130), 0, Qt::DotLine));
  
  // Add data:
  QVector<double> fossilData, nuclearData, regenData;
  fossilData  << 0.86*10.5 << 0.83*5.5 << 0.84*5.5 << 0.52*5.8 << 0.89*5.2 << 0.90*4.2 << 0.67*11.2;
  nuclearData << 0.08*10.5 << 0.12*5.5 << 0.12*5.5 << 0.40*5.8 << 0.09*5.2 << 0.00*4.2 << 0.07*11.2;
  regenData   << 0.06*10.5 << 0.05*5.5 << 0.04*5.5 << 0.06*5.8 << 0.02*5.2 << 0.07*4.2 << 0.25*11.2;
  fossil->setData(ticks, fossilData);
  nuclear->setData(ticks, nuclearData);
  regen->setData(ticks, regenData);
  
  // setup legend:
  customPlot->legend->setVisible(true);
  customPlot->axisRect()->insetLayout()->setInsetAlignment(0, Qt::AlignTop|Qt::AlignHCenter);
  customPlot->legend->setBrush(QColor(255, 255, 255, 100));
  customPlot->legend->setBorderPen(Qt::NoPen);
  QFont legendFont = font();
  legendFont.setPointSize(10);
  customPlot->legend->setFont(legendFont);
  customPlot->setInteractions(QCP::iRangeDrag | QCP::iRangeZoom);

//这里可以显示文本(思路)
//  for (int i = 0; i < fossil->dataCount(); ++i) {
//      QCPItemText *text = new QCPItemText(customPlot);
//      text->setPositionAlignment(Qt::AlignTop|Qt::AlignHCenter);

//      double key = regen->data()->at(i)->key;
//      double value = regen->getStackedBaseValue(regen->data()->at(i)->key, true)+ regen->data()->at(i)->value;
//      text->position->setCoords(key, value); // 将文本位置设置在 bar 的正上方
//      QString valueStr = QString::number(regen->data()->at(i)->value); // 将数值转换为字符串
//      text->setText(valueStr); // 设置文本内容
//      text->setFont(QFont(font().family(), 10)); // 设置文本字体大小
//      text->setPen(QPen(Qt::black)); // 设置文本颜色
//  }
}

效果