如何在VC ++ 6.0中模拟可变参数宏? [英] How to mimic variadic macro in VC++6.0?

问题描述

在 VS2010 中，我编写了以下可变参数宏以将信息转储到文件中.

In VS2010, I wrote the following variadic macros to dump out information to files.

#define INDENT(fp, indent) for(size_t __i = 0; __i < (indent); ++__i) fprintf((fp), "  ")
// IND_FP = indented fprintf.
// This macro uses two IMPLICIT parameters.
// 1. (FILE *)fp is a pointer to the output file.
// 2. (size_t)indent specifies the indentation level.
#define IND_FP(format, ...) do{ INDENT(fp, indent); fprintf(fp, format, __VA_ARGS__); }while(0)

这些宏经常出现在我的程序中.

These macros frequently occur in my program.

void CMAP::dump_info(FILE *fp, size_t indent){
  IND_FP("<cmap tableVersion=\"0x%08x\" numberOfEncodingTables=\"%d\">\n",
    table_version_number, num_encoding_tables);
  //...
  IND_FP("</cmap>\n");
}

遗憾的是，现在我必须将代码迁移到以前的IDE( VC ++ 6.0 )，后者不不支持可变宏.我写了一个可变参数函数.

Sadly, now I have to migrate my code to the antediluvian IDE, VC++6.0, which does NOT support variadic macro. I wrote a variadic function instead.

void IND_FP(FILE *fp, size_t indent, char *format, ...){
  INDENT(fp, indent);
  va_list arg_ptr;
  va_start(arg_ptr, format);
  vfprintf(fp, format, arg_ptr);
  va_end(arg_ptr);
}

但是我必须将数十行代码(如果不是几百行)从IND_FP(format, ...)更改为IND_FP(fp, indent, format, ...).

But I have to change the tens if not hundreds lines of code from IND_FP(format, ...) to IND_FP(fp, indent, format, ...).

是否有任何宏技巧可以帮助我?还是我最好使用显式参数并习惯冗余?

Is there any trick of macro that can help me out? Or I'd better use explicit arguments and get used to redundancy?

推荐答案

您可以通过不使用它们来获得圆形等角​​函数.使用ofstream代替FILE *.像这样

You could get round variadics by not using them. Use ofstream instead of FILE*. Something like this

#define LOGGER(logfile,loginfo)  logfile << loginfo << std::endl

假设您已声明一个名为logfile的流.对于简单的事情，您可以使用

Say you've declared an ofstream called logfile. For simple things, you can use

LOGGER(logfile, x);

如果您想变得更复杂，可以使用

If you wish to get more complex, you could use

LOGGER(logfile, "x = " << x << "  b=" << b);

对于缩进，您可以使用全局

For the indent, you could use a global

// declaration
char spaces[128];
...
// Initialization
memset(spaces, ' ', sizeof(spaces));

#define LOGGER(logfile,indent,loginfo) \
    spaces[indent] = '\0'; \
    logfile << spaces << loginfo << std::endl; \
    spaces[indent] = ' '

以同样的方式，如果您希望缩进3

So in the same way, if you wish to indent by 3

LOGGER(logfile, 3, "x=" << x << "   y=" << y << "   z=" << z);

C ++<<在格式化方面不如printf优雅，但可以解决使用variadics的问题.

C++ << is not as elegant as printf for formatting but it will get you round the problem of using variadics.

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