在预处理器宏中检测空参数 [英] Detecting null parameter in preprocessor macro

问题描述

我在香草 C 中具有以下宏功能:

I have the following macro function in vanilla C:

#define GLOG(format_string, ...) { \
  const char *file = strrchr(__FILE__, '/'); \
  char format[256] = "%s:%s!%d\t"; \
  strncat(format, format_string, 248); \
  strcat(format, "\n"); \
  printf(format, __FUNCTION__, file ? file : __FILE__, __LINE__, ##__VA_ARGS__); \
}

这使我可以打印一条调试消息，其中包含当前函数，文件和行号，例如

which lets me print a debug message containing the current function, file and line number, e.g.

GLOG("count=%d", count);

可能打印

do_count:counter.c!123  count=456

1. 如果调用者省略format_string，如何修改函数以打印所有局部变量?例如

1. How can I modify the function to print all local variables if caller omits format_string? e.g.

GLOG();

可能打印

do_count:counter.c!123  count=456, message="Hello world", array=[7, 8] structure={ptr=0xACE0FBA5E, coord={x=9, y=0}}

如果不可能，如何修改它以仅打印当前函数，文件和行号?例如

If that's not possible, how can I modify it to print just the current function, file and line number? e.g.

do_count:counter.c!123

按原样，这将返回错误:

As is, this returns an error:

错误:，"令牌之前的预期表达式

error: expected expression before ‘,’ token

strncat行很简单

strncat(format, , 248);

推荐答案

首先，似乎无法通过进程本身在运行时检查所有局部变量，因为C没有任何反映方式.

First, inspecting all the local variables at runtime by the process itself seems impossible because C doesn't have any means for reflection.

第二，如果您这样编写日志记录宏，将会更好:

Second, you would be much better off if you wrote the logging macro like that:

#include <stdio.h>

#define STRINGIFY(x) #x
#define TOSTRING(x) STRINGIFY(x)

#define GLOGF(fmt, ...) \
  printf("%s:%s " fmt "\n", __func__, __FILE__ "!" TOSTRING(__LINE__), ##__VA_ARGS__)

int main (void) {
  /* main:test.c!xx count=5 */
  GLOGF("count=%d", 5);
  /* main:test.c!xx */
  GLOGF();
  return 0;
}

这很简单，并且由于在编译时将字符串串联在一起，因此不会产生任何额外的运行时开销.

It is simpler and doesn't incur any additional runtime overhead since the string is concatenated at compile-time.

还要注意，我使用了__func__而不是__FUNCTION__，因为后者是非标准的.

Also note that I have used __func__ instead of __FUNCTION__, because the latter is non-standard.

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