Question

I’ve been working with OpenCV, and some of the example code I’ve seen uses the following to read in a filename. I understand that argc is the number of command line arguments that were passes, and argv is a vector of argument strings, but can someone clarify what each part of the following line does? I’ve tried searching this but haven’t found many results. Thanks.

const char* imagename = argc > 1 ? argv[1] : "lena.jpg";

Thanks.

Answer 1

The example shows the use of the ternary operator.

const char* imagename = argc > 1 : argv[1] : “lana.jpg”
By ternary you can say that this expression has three members.

First member is a condition expression

Second member is the value that could be assigned to imagename if conditional expression is true.

Third member is the value that could be assigned to imagename if conditional expression is false.

This example can be translated to:

const char* imagename;
if(argc > 1)
    imagename = argv[1];
else
    imagename = "lana.jpg";