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#define BUFFER_SIZE 256 as a textual assignment giving the symbol BUFFER_SIZE a value "256". Symbols defined with cpp are traditionally given upper case names to distinguish them from C identifiers. This symbol can be used later in the input, as in char input_buffer[BUFFER_SIZE]; This use of cpp to name constants, rather than writing these {magic numbers} inline, makes a program easier to read and maintain, especially if there is more than one occurrence of BUFFER_SIZE all of which must all have the same value. Cpp macros can have parameters: #define BIT(n) (1<<(n)) This can be used with any appropriate actual argument: msb = BIT(nbits-1); Note the parentheses around the "n" in the definition of BIT. Without these, operator precedence might mean that the expression スポンサード リンク
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