CERN -> IPT Group -> FrameMaker at CERN
Information Service User's Guide

2.3 Reading information

2.3.1 Getting the last value of the information

Once an information is published any other application can read it. "Listing 2.6" shows how a C++ program can get the latest information value. This program uses the getValue method of the ISInfoDictionary class in order to get the value of the specific information from the IS.

Listing 2.6   Reading last information value
1: #include <is/infoT.h>
2: #include <is/infodictionary.h>
3: #include <ipc/core.h>
4:
5: int main ( int ac, char ** av ){
6: // Initialise communication library
7: IPCCore::init( ac, av );
8:
9: // Create the instance of partition
10: IPCPartition partition("MyPartition");
11:
12: // Create the IS dictionary the specific partitition
13: ISInfoDictionary dict(partitition);
14:
15: // Create the instances of the information that will be read
16: ISInfoInt voltage;
17: ISInfoFloat temperature;
18:
19: // Read information
20: dict.getValue( "MyServer.DeviceVoltage", voltage );
21: dict.getValue( "MyServer.DeviceTemperature", temperature );
22: return 0;
23: }

2.3.2 Reading specific value of the objects history

Instead of retrieving the most recent value of the information object, it's also possible to get a specific value form the object's history by providing the tag ID of that value. "Listing 2.7" shows how to do that. This program uses another variant of the getValue method of the ISInfoDictionary class which takes the value ID as its second parameter.

Listing 2.7   Reading specific history value of the information
1: #include <is/infoT.h>
2: #include <is/infodictionary.h>
3: #include <ipc/core.h>
4:
5: int main ( int ac, char ** av ){
6: // Initialise communication library
7: IPCCore::init( ac, av );
8:
9: // Create the instance of partition
10: IPCPartition partition("MyPartition");
11:
12: // Create the IS dictionary the specific partitition
13: ISInfoDictionary dict(partitition);
14:
15: // Create the instances of the information that will be read
16: ISInfoInt voltage;
17:
18: // Read information
19: dict.getValue( "MyServer.DeviceVoltage", 2, voltage );
20: return 0;
21: }

2.3.3 Retrieving information history

"Listing 2.8" shows how a C++ program can get the all information values, including the latest value and also all or some history values This program uses the getValues template method of the ISInfoDictionary class in order to get the all the value of the specific information from the IS.

Listing 2.8   Reading history of information
1: // include the IS header file
2: #include <is/infoT.h>
3: #include <is/infodictionary.h>
4: #include <ipc/core.h>
5:
6: int main ( int ac, char ** av ){
7: // Initialise communication library
8: IPCCore::init( ac, av );
9:
10: // Create the instance of partition
11: IPCPartition partition("MyPartition");
12:
13: // Create the IS dictionary instance
14: // using the partitition object as parameter
15: ISInfoDictionary dict(partitition);
16:
17: // Create the instances of the information
18: // that will be red
19: std::vector<ISInfoInt> voltages;
20: std::vector<ISInfoFloat> temperatures;
21:
22: // Read information history
23: dict.getValues( "MyServer.DeviceVoltage", voltages );
24: dict.getValues( "MyServer.DeviceTemperature", temperatures );
25:
26: for ( size_t i = 0; i < voltages.size(); i++ )
27: std::cout << "Voltage [" << i << "] = " << voltages[i] << std::endl;
28:
29: for ( size_t i = 0; i < voltages.size(); i++ )
30: std::cout << "Temperatures [" << i << "] = " << temperatures[i] << std::endl;
31:
32: return 0;
33: }

The lines 21-27 shows how to read all the history values for the "MyServer.DeviceVoltage" and "MyServer.DeviceTemperature" information respectively. The history values are stored in the vector, which is provided as second argument of the getValues function. The information values in the resulting vector are sorted by their time with the most recent value in the first element of the vector.

The list of history values might be long and one may want to read only the last N history values instead of reading all of them. This can be done by using the 3d parameter of the getValues function as it is shown in "Listing 2.9".

Listing 2.9   Reading last 10 values from information history
1: // include the IS header file
2: #include <is/infoT.h>
3: #include <is/infodictionary.h>
4: #include <ipc/core.h>
5:
6: int main ( int ac, char ** av ){
7:
8: ...
9:
10: std::vector<ISInfoInt> voltages;
11: std::vector<ISInfoFloat> temperatures;
12:
13: // Read the last 10 history values information
14: dict.getValues( "MyServer.DeviceVoltage", voltages, 10 );
15: dict.getValues( "MyServer.DeviceTemperature", temperatures, 10 );
16:
17: return 0;
18: }

The 3d parameter od the getValues function can be negative (its default value is -1), in which case the function retrieves all available history values for the given information object. Passing any positive value N to the getValues function call will result in reading at most the N most recent information values. If the current history size is less than N, then the number of elements in the vector will be equal to the current history size.

2 July 1998 - WebMaster
Copyright © CERN 1998