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Defining Macros with Parameters

Defining Macros with Parameters. Defining constant macro # define macro_name value For example: # define KMS_PER_MILE 1.609 Defining macro with parameters # define macro_name(parameter lis) macro body For example: # define SQUARE (n) ((n) * (n)). Program Using a Macro with Parameters.

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Defining Macros with Parameters

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  1. Defining Macros with Parameters Defining constant macro # define macro_name value For example: # define KMS_PER_MILE 1.609 Defining macro with parameters # define macro_name(parameter lis) macro body For example: # define SQUARE(n)((n) * (n))

  2. Program Using a Macro with Parameters /* Shows the definition and use of a macro */ #include <stdio.h> #define LABEL_PRINT_INT(label, num) \ printf("%s = %d", (label), (num)) int main(void) { int r = 5, t = 12; LABEL_PRINT_INT("rabbit", r); printf(" "); LABEL_PRINT_INT("tiger", t + 2); printf("\n"); return(0); } rabbit = 5 tiger = 14

  3. Macro Expansion LABEL_PRINT_INT(“tiger”, t+2) Second macro call in the main LABEL_PRINT_INT(label, num) Parameter matching: tiger t+2 printf(“%s = %d”, (label), (num)) parameter replacement in body printf(“%s = %d”, (“tiger”), (t+2))

  4. Rules for Defining Macros with parameters • Same as constant macro there is no “;” at the end of macro definition • To extend a macro over multiple lines, all except for the last line must end with backslash character “/” • Operators with side effect should not be used as macro arguments. For example #define RT(++a) is wrong

  5. Rules for Defining Macros with parameters • Using the parenthesis for the formal parameters in Macro body is required to avoid the effect of operator precedence in macro expansion. For example: Version 1 Version 2 #define SQUARE(n) n * n #define SQUARE(n) ((n) * (n)) SQUARE(x + y) SQUARE(x + y) becomes becomes x + y * x + y ((x + y) * (x + y)) Problem: multiplication done before addition in version 1, also. SQUARE(m) / SQUARE(n) SQUARE(m) / SQUARE(n) becomes becomes m * m / n * n ((m) * (m)) / ((n) * (n)) Therefore, the result produced by version 1 is wrong

  6. More examples of Macro with Parameters • # define ROOT1(a, b, c) \ ((-(b) + sqrt((b) * (b) – 4 * (a) * (c))) / (2 * (a))) Can be used in the main as r = ROOT1(n1, n2, n3); • # define INDEXED-FOR(ct, st, end) \ for ((ct) = (st); (ct) < (end); ++(ct)) Can be used in the main as INDEXED_FOR(i,0,X_MAX) printf(“x[%2d] = %6.2f\n”, i, x[i]);

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