#define导致“预期的主要表达式”错误 [英] #define causes an "expected primary-expression" error

问题描述

#define N 10;

int main()
{
    int x;

    for (int i=0; i<N; i++)
        x = i;

    return 0;
}

用g ++编译的结果：

Result of compiling this in g++:

test-define.cpp: In function ‘int main()’:
test-define.cpp:7:22: error: expected primary-expression before ‘;’ token
test-define.cpp:7:22: error: expected ‘)’ before ‘;’ token
test-define.cpp:7:24: error: name lookup of ‘i’ changed for ISO ‘for’ scoping [-fpermissive]
test-define.cpp:7:24: note: (if you use ‘-fpermissive’ G++ will accept your code)
test-define.cpp:7:27: error: expected ‘;’ before ‘)’ token

但它会编译当我将第7行更改为时很好（int i = 0; i< 10; i ++）。

But it compiles fine when I change line 7 to for (int i=0; i<10; i++).

为什么是这个，我该如何使用 #define 指令来完成所需的操作？

Why is this and how can I use the #define directive to accomplish what I want?

推荐答案

删除分号-会很好-替换中包含分号

Remove the semicolon - you will be good - the semicolon is included in the substitution

有时，让编译器仅运行预处理器很有用。使用gcc / g ++，您可以执行以下操作

Sometimes it is useful to get the compiler to run the preprocessor only. With gcc/g++ you can do something like

gcc -E file.c > result.txt

这将向您展示宏的扩展方式（提示从文件末尾开始，工作）

This will show you how the macro expanded (hint start at the end of the file and work up)

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