callandreturn

Call and return, or call-and-return control flow, is the fundamental mechanism by which a program transfers execution from a caller to a subroutine and later resumes at the point of departure after the subroutine finishes. A call passes arguments to the callee and transfers control to the subroutine’s entry point; a return transfers control back to the caller and may supply a result.

Implementation typically relies on a call stack. The caller pushes a return address and arguments according to a calling convention, then jumps to the subroutine. The callee creates a stack frame for its local variables and parameters, executes, and, when finished, places any return value, restores the previous stack frame, and returns to the saved address. The exact mechanics—how arguments are passed, where the return address is stored, and how stack frames are managed—vary by language, compiler, and hardware.

Tail calls are a notable optimization in which the callee immediately returns to the caller, allowing the current stack frame to be replaced rather than grown. When supported, tail-call optimization enables efficient recursion and long chains of calls.

Call and return is distinct from other control-flow constructs such as coroutines, generators, or asynchronous callbacks, though many languages combine them. It also interacts with exception handling and stack unwinding; errors may bypass normal returns and trigger unwinding of the call stack.

Historically, subroutine calls emerged in early languages such as Fortran and Algol and became the dominant method for structuring programs in imperative languages like C, Java, and many others. The precise behavior is determined by the language’s calling conventions and the underlying hardware architecture.