12/1/2023 0 Comments Read only macro in c![]() ![]() Unlike an ordinary C macro, however, an _asm macro cannot return a value. To prevent errors, use old-style C comments ( /* comment */) in _asm blocks defined as macros.Īn _asm block written as a C macro can take arguments. The same is true of single-line C or C++ comments ( // comment). This causes problems in macros because the compiler ignores everything after the comment, all the way to the end of the logical line. Without the closing brace, the compiler cannot tell where assembly code stops, and it sees C or C++ statements after the _asm block as assembly instructions.Īssembly-style comments that start with a semicolon ( ) continue to the end of the line. If you omit them, the compiler can be confused by C or C++ statements on the same line to the right of the macro invocation. ![]() Because a block defined as a macro is one logical line, you must separate each instruction with _asm. ![]() The only statement separators recognized in _asm blocks are the newline character and _asm keyword. The third and fourth _asm keywords are needed as statement separators. They are needed, however, because the macro expands into a single line: _asm /* Port output */ To illustrate, the following example defines a simple macro: #define PORTIO _asm \Īt first glance, the last three _asm keywords seem superfluous. Use old-style C comments ( /* comment */) instead of assembly-style comments ( comment) or single-line C comments ( // comment). Put the _asm keyword in front of each assembly instruction. To create trouble-free macros, follow these rules: C macros offer a convenient way to insert assembly code into your source code, but they demand extra care because a macro expands into a single logical line. ![]()
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