c - Weird #define declaration, can't understand to what it expands -

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i have #define statement in legacy code i'm inspecting in c.

#define step(x)         case x: step ## x : wpan_startup_step = x;

this macro replace cases in big switch state machine. can't understand what's going on in macro. expand ?

## concatenation, means result this:

step(1)  case 1: step1: wpan_startup_step = 1;

or example:

step(v)  case v: stepv: wpan_startup_step = v;

this macro not make sense me, since generates x: stepx: maybe usage example clarify this.

if want see expansion of macro use: gcc -e program.c

also place learn macros: http://gcc.gnu.org/onlinedocs/cpp/macros.html


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