c - 宏编译

Question

我在编译代码时收到这些错误消息。我很困惑。我使用 clang 编译器，代码是用 C 编写的。宏应该交换两个 t 类型的参数。

Documents/program7.c:5:5: error: expected ')'
( t type = x; x = y; y = type; )
    ^
Documents/program7.c:5:1: note: to match this '('
( t type = x; x = y; y = type; )
^
Documents/program7.c:5:3: warning: type specifier missing, defaults to 'int'
      [-Wimplicit-int]
( t type = x; x = y; y = type; )
  ^
Documents/program7.c:5:15: warning: type specifier missing, defaults to 'int'
      [-Wimplicit-int]
( t type = x; x = y; y = type; )
              ^
Documents/program7.c:5:19: error: use of undeclared identifier 'y'
( t type = x; x = y; y = type; )
                  ^
Documents/program7.c:5:22: warning: type specifier missing, defaults to 'int'
      [-Wimplicit-int]
( t type = x; x = y; y = type; )
                     ^
Documents/program7.c:5:26: error: use of undeclared identifier 'type'
( t type = x; x = y; y = type; )
                         ^
Documents/program7.c:5:32: error: expected identifier or '('
( t type = x; x = y; y = type; )

代码:

#include <stdio.h>

#define SWAP(t,x,y) \

( t type = x; x = y; y = type; )

int main()
{
    int x, y;
    x = 2, y = 10;

    swap(int, x, y);

    printf("%d %d\n", x, y);

    return 0;
}

Answer 1

替换您的:

#define SWAP(t,x,y) \

( t type = x; x = y; y = type; )

与

#define SWAP(t,x,y) \
do { t type = x; x = y; y = type; } while (0)

并更改调用:

swap(int, x, y);

至

SWAP(int, x, y);

宏定义中的一些注意事项:\ 之后不能有空行，而且 () 只能在表达式之间使用，不能在语句之间使用。