C4425: ## in substitution list must be preceded and followed by a symbol

[FATAL]

There is a problem with the string concatenation ## operator during preprocessing, because there is no legal name as formal parameter specified.

  #define cat(a,b) a ##

  

  void foo(void) {

  

    i = cat(3,3);

  

  }

  

Check your macro definition or usage. Generate a preprocessor output (option -Lp) to find the problem.