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4.5.2 Nested Macro Definitions

Generally speaking, Dynamic C expands macro calls recursively until they can expand no more. Another

way of stating this is that macro definitions can be nested.

The exceptions to this rule are

1. Arguments to the # and ## operators are not expanded.

2. To prevent infinite recursion, a macro does not expand within its own expansion.

The following complex example illustrates this.

The code

will expand first to

then to

and finally to

#define A B

#define B C

#define uint unsigned int

#define M(x) M ## x

#define MM(x,y,z) x = y ## z

#define string something

#define write( value, fmt )\

printf( #value "=" #fmt "\n", value )

uint z;

M (M) (A,A,B);

write(string, %s);

unsigned int z; // simple expansion

MM (A,A,B); // M(M) doesn’t expand recursively

printf( "string" "=" "%s" "\n", string ); // #value  "string" #fmt  "%s"

unsigned int z;

A = AB; // from A = A ## B

printf( "string" "=" "%s" "\n", something );

// string  something

unsigned int z;

B = AB; // A  B

printf( "string=%s\n", something ); // concatenation

unsigned int z;

C = AB; // B  C

printf("string = %s\n", something);