CPP宏：提供实例化/调用次数的计数器 [英] CPP Macro: Counter that gives number of instantiations/calls

问题描述

我想拥有一个 C 预处理器宏，到目前为止，该宏知道该宏的实例化/宏调用的数量。
示例：

I want to have a C preprocessor macro that knows the number of instantiations/macro calls of this macro so far. Example:

int main() {
  printf("%d\n", MACRO());
  printf("%d\n", MACRO());
}

应打印

0
1

类似这样的可能？

请注意，将其转发给以下建议的功能还不够。
它应在以下环境下工作：

Note that it is not enough to forward this to a function as proposed below. It should work in the following context:

// global variable
std::vector<bool> calls_hit;

#define OTHER_MACRO() \
{ \
    const int counter = MACRO(); \
    calls_hit.resize(std::max(calls_hit.size(), counter)); \
    calls_hit[counter] = true; \
}

推荐答案

我碰巧有一种与 __ COUNTER __ 类似（使用）的解决方案，但不仅限于单个计数器-您可以根据需要定义多个计数器。

I happen to have a solution that is similar (in usage) to __COUNTER__ , but is not limited to single counter - you can define many counters as you like.

此功能使用了gcc特有的功能，但应该可以在其他工具链中执行类似的操作。

This one uses gcc-specific feature, but should be able to do similar in other toolchain.

static int getpos(int lineno); // forward declaration

#define MY_COUNTER ({                                                    \
            static const int mark __attribute__((LSEG,used)) = __LINE__; \
            getpos(__LINE__);                                            \
})

static int __attribute__((noinline)) getpos(int lineno) {
    static const int mark __attribute__((LSEG,used)) = __LINE__;
    const int *p = &mark;
    int i;
    for (i = 0; *p++ != lineno; i++);
    return i;
}

在上面的代码中，LSEG扩展为section（。rodata.line01234 ）是根据 __ LINE __ 信息生成的。

In above code, LSEG expands to something like section(".rodata.line01234") generated from __LINE__ information.

以下是其工作原理的说明：

Here's an expalanation of how this works:

1. 每当您使用MY_COUNTER宏时，它将被2个代码片段代替：1）将 __ LINE __ 值压入的代码LSEG宏指定的内存段，以及2）调用getpos（ __ LINE __ ）函数的代码，该函数返回写入给定行的调用数。


2. LSEG宏扩展到具有行号的段说明符（例如：section（。rodata.line01234））。


3. 通过指定链接器以字母顺序对段进行排序（-Wl， --sort-segment = name与GNU ld），可以确保所有附加的 __ LINE __ 值均按使用顺序排列。


4. 在运行时，getpos（ __ LINE __ ）函数扫描内存段，并返回写到给定行的调用数。

1. Whenever you use MY_COUNTER macro, it is replaced with 2 code fragments: 1) code that pushes __LINE__ value to memory segment specified by LSEG macro, and 2) code that calls getpos(__LINE__) function, which returns # of calls written up to given line.
2. LSEG macro expands to section specifier with a line number (ex: section(".rodata.line01234")).
3. By specifying linker to sort segment alphabetically (-Wl,--sort-segment=name with GNU ld), you can be sure all appended __LINE__ values are in order they were used.
4. At run-time, getpos(__LINE__) function scans through the memory segment, and returns # of calls written up to given line.

希望这会有所帮助。

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