1. ECE 103 Engineering Programming Chapter 37 C Macro Parameters
Herbert G. Mayer, PSU CS
Status 6/4/2014
Initial content copied verbatim from
ECE 103 material developed by
Professor Phillip PSU ECE

2. Syllabus Defining a Parameterized Macro
Parameterized Macros vs. C Functions

3. Defining a Parameterized Macro
Similar to a C function, preprocessor macros can be defined with a parameter list.
The macro’s parameters do not require data types to be specified.
Syntax:
#define MACRONAME(parameter_list) text
No white space is allowed between the name of the macro and the left parenthesis. 2

4. Parameters in the parameter_list are separated by commas. Example:
#define MAXVAL(A,B) ((A) > (B)) ? (A) : (B)
#define PRINT(e1,e2) printf(”%c\t%d\n”,(e1),(e2));
#define putchar(x) putc(x, stdout)
Arguments passed to the parameterized macro are substituted verbatim into the corresponding parameters. 3

5. Care must be taken to avoid side-effects
Care must be taken to avoid side-effects. Use parentheses to force a particular interpretation.
Example:
/* This has potential side-effects */
#define PROD1(A,B) A * B
PROD1(1+3,2) → 1+3 * 2
/* Use parentheses as needed */
#define PROD2(A,B) (A) * (B)
PROD2(1+3,2) → (1+3) * (2) 4

6. Example: #include <stdio.h> #include <math.h>
#define EVERYFIFTH(n) ((n) % 5 == 0)
int main (void) {
int k;
for (k = 0; k < 100; k++)
if (EVERYFIFTH(k)) /* Silly, but it does work */
printf("%3d %.3f\n", k, sqrt(k));
return 0; } 5

7. Parameterized Macros vs. C Functions
Since macro expansion is done at compile-time, there is no function call overhead at runtime.
There is no type checking performed for macros, which is useful if generic data types are desired for arguments.
Unlike a C function, parameterized macros have no concept of local variables. 6