how to pass data from terminal to a program? - c++

Question

i am using a GPS reciever that will print GPS message contiuously in terminal using a C++ program like this
Latitude:13.3 Longitude:80.25
Latitude:13.4 Longitude:80.27
Latitude:13.5 Longitude:80.28
I want to take this data inside my c++ program (QT Application)
Below is my full program code
void QgsGpsPlotPluginGui::on_buttonBox_accepted()
{
QString myPluginsDir = "usr/lib/qgis/plugins";
QgsProviderRegistry::instance(myPluginsDir);
QgsVectorLayer * mypLayer = new QgsVectorLayer("/home/mit/Documents/Dwl/GIS DataBase/india_placename.shp","GPS","ogr");
QgsSingleSymbolRenderer *mypRenderer = new
QgsSingleSymbolRenderer(mypLayer->geometryType());
QList <QgsMapCanvasLayer> myLayerSet;
mypLayer->setRenderer(mypRenderer);
if (mypLayer->isValid())
{
qDebug("Layer is valid");
}
else
{
qDebug("Layer is NOT valid");
}
// Add the Vector Layer to the Layer Registry
QgsMapLayerRegistry::instance()->addMapLayer(mypLayer, TRUE);
// Add the Layer to the Layer Set
myLayerSet.append(QgsMapCanvasLayer(mypLayer, TRUE));
QgsMapCanvas * mypMapCanvas = new QgsMapCanvas(0, 0);
mypMapCanvas->setExtent(mypLayer->extent());
mypMapCanvas->enableAntiAliasing(true);
mypMapCanvas->setCanvasColor(QColor(255, 255, 255));
mypMapCanvas->freeze(false);
QgsFeature * mFeature = new QgsFeature();
QgsGeometry * geom = QgsGeometry::fromPoint(*p);
QGis::GeometryType geometryType=QGis::Point;
QgsRubberBand * mrub = new QgsRubberBand (mypMapCanvas,geometryType);
QgsPoint * p = new QgsPoint();
double latitude =13.3;
double longitude = 80.25;
p->setX(latitude);
p->setY(longitude);
mrub->setToGeometry(geom,mypLayer);
mrub->show()
}
In the above code i have manually entered the value for Latitude and Longitude like this,
double latitude =13.3;
double longitude = 80.25;
p->setX(latitude);
p->setY(longitude);
but i need to get these value from terminal.
Both program are written in c++ but they belong to different framework.

Answer 1

I assume that your library doesn't have an API you can use.
Then one fairly straight forward way to integrate them would be to use pipes.
You can quickly do something like
gps_program | qt_program
And now you get the coordinates via stdin.
The more complex way to set it up is using exec and fork. You create pipe objects, then fork and run using exec the gps_programon one of the branches. This you can do entirely in your code without depending on bash or something like it. You still have to parse the data coming from the pipe the same way.

Answer 2

Just create a pipe:
#include <cstdio>
#include <iostream>
#define WWRITER 0
#if WWRITER
int main() {
while (true) {
std::cout << "Latitude:13.3 Longitude:80.25";
}
return 0;
}
#else
int main() {
FILE* fp = popen("Debug/Writer", "r");
if(fp == 0) perror(0);
else {
const std::size_t LatitudeLength = 9;
const std::size_t LongitudeLength = 10;
char latitude_name[LatitudeLength+1];
char longitude_name[LongitudeLength+1];
double latitude;
double longitude;
while(fscanf(fp, "%9s%lf%10s%lf",
latitude_name,
&latitude,
longitude_name,
&longitude) == 4)
{
std::cout << "Values: " << latitude << ", " << longitude << std::endl;
}
pclose(fp);
}
return 0;
}
#endif
Note: The example runs endlessly.

Answer 3

+1 to Sorin's answer, makes this nice and easy passing stdout to stdin :) but assuming you are running in linux / cigwin?
But if you have access to both program codes then a nicer solution is to use UdpSockets (or maybe Tcp, but Udp is simpler) and pass the data between programs in this way... not sure how big/long-term your solution needs to be but if you want to integrate them in a "long-term" and more maintainable way this would be a better approach.