The C++ Standard Library

This section briefly discusses a few classes provided by the C++ Standard Library that we will make use of in our RtMidi programs.

C++ Standard Output

We will make use of the C++ standard output stream, std::cout, to print messages from a running program to a terminal window. This will typically be done to display incoming MIDI message information.

• The std::cout object can be used to write formatted text strings to standard output, typically a terminal window from which a program is invoked.

• For our purposes, the insertion operator («) is sufficient for organizing the output data.

  #include <iostream>
  
    std::cout << "Hello World!" << std:endl;
    int myint = 55;
    std::cout << "My integer has the value of " << myint << std::endl;
  

• Note the use of the std::endl function to insert a newline and flush the output stream.

The Vector Class

• Various “container” classes are provided in the C++ Standard Library, including list, queue, deque, vector, map, stack and set.

• The container classes are optimized for specific behavior types. For example, a list allows constant time insert and erase operations anywhere in a sequence, while a deque supports random access iterators and efficient insertion/deletion at both beginning and end.

• A vector supports efficient random-access iterators but is not as efficient as a list for random insertion/deletion of elements.

• The vector class does no bounds checking when using the element access operator [].

• C++ vectors can be initialized from other C++ vectors but not with C-style array initialization lists (except in recent versions of C++).

• In RtMidi, we will use the data type std::vector<unsigned char> to send and receive MIDI bytes from / to MIDI ports.

  #include <vector>
  #include <iostream>
  
  int main()
  {
    std::vector<unsigned char> bytes;      // zero-length vector of chars
    std::vector<int> ints1( 5 );           // 5 ints initialized to default value
    std::vector<float> floats1( 5, 2.0 );  // 5 floats initialized to 2.0
    std::vector<int> ints2( ints1 );       // copy of "ints1" vector
  
    bytes.push_back( 144 );                // create a list of 3 byte values
    bytes.push_back( 64 );
    bytes.push_back( 24 );
  
    bytes[0] = 128;                        // modify the first value in the vector
  
    for ( unsigned int i=0; i<bytes.size(); i++ )
      std::cout << "bytes[" << i << "] = " << (int) bytes[i] << std::endl;
  
    bytes.clear();                         // remove all the elements in the vector
    std::cout << "bytes now holds " << bytes.size() << " elements." << std::endl;
  
    bytes.resize( 2 );                     // resize the vector to the specified number of elements
    std::cout << "bytes now holds " << bytes.size() << " elements." << std::endl;
  
    bytes[3] = 79;     // ERROR: attempt to write a value to the 4th element, which doesn't exist!!!
  
    return 0;
  }