Question

Wikipedia has a definition for a control flow graph. I’ve also heard terminology thrown around referring to ‘call (flow?) graph’, but can’t find any relevant resources. What is the relationship between the two?

Answer 1

Wikipedia defines a call graph as a representation of the calling relationships between subroutines in a program. In a call graph, an edge between two nodes f and g:

      f --> g

represents the fact that subroutine f calls subroutine g. A call graph gives an inter-procedural view of a program.

A control flow graph (CFG) provides finer “details” into the structure of the program as a whole, and of the subroutines in particular. For instance, the CFG of a subroutine f will make explicit all of the paths that are induced by a conditional branch:

                             / branch1 \
    begin --> condition -->             --> codeblock --> g --> end
                             \ branch2 /

This kind of CFG is used to build an intra-procedural view of a subroutine.