是可能写到控制台没有stdlibs？ c / c ++ [英] is it possible write to console without stdlibs? c/c++

问题描述

我在arm微处理器上编程，并尝试通过UART调试打印语句。我不想添加 stdlibs 只是为了调试。有没有办法打印到控制台，不用 stdio.h / iostream.h ？我可以写我自己的 printf（）？

I am programming on an arm microprocessor and am trying to debug using print statements via UART. I do not want to add stdlibs just for debugging. Is there a way to print to the console without stdio.h/iostream.h ? Is it possible for me to write my own printf()?

或者我可以使用DMA控制器并直接写入UART。但我想避免这是可能的。使用内置的测试函数echo或
remote loop-back我知道我正确配置了UART。

Alternatively I can do this using a DMA controller and writing to the UART directly. However I would like to avoid that is possible. Using the built in test function "echo" or "remote loop-back" I know I have the UART configured properly.

推荐答案

简单的答案：是的，完全可以做到你的两个解决方案。

Short answer: Yes, it's entirely possible to do both of your solutions.

如果您要支持所有的数据类型和格式，printf函数非常复杂。但是编写可以输出一个字符串或一个整数在几个不同的基础（大多数人只需要十进制和十六进制，但八进制可能只有添加另外3-4行代码一旦你有十进制和十六进制）不是很难。

The printf function is quite complex if you want to support all of the data types and formats. But it's not that hard to write something that can output a string or an integer in a few different bases (most people only need decimal and hex, but octal probably only adds another 3-4 lines of code once you have decimal and hex).

通常，printf是这样写的：

Typically, printf is written like this:

 int printf(const char *fmt, ...)
 {
     int ret;
     va_list args; 

     va_start(args, fmt)
     ret = do_xprintf(outputfunc, NULL, fmt, args); 
     va_end(args);
     return ret;
}

然后 do_xprintf（）对所有变体（printf，sprintf，fprintf等）执行所有的工作

And then the do_xprintf() does all the hard work for all variants (printf, sprintf, fprintf, etc)

int do_xprintf(void (*outputfunc)(void *extra, char c), void *extra, const char *fmt, va_list args)
{
    char *ptr = fmt;
    while(1)
    {
       char c = *ptr++;

       if (c == '%')
       {
            c = *ptr++; // Get next character from format string. 
            switch(c)
            {
               case 's': 
                  char *str = va_arg(args, const char *);
                  while(*str)
                  {
                      count++;
                      outputfunc(extra, *str);
                      str++;
                  }
                  break; 
               case 'x': 
                  base = 16;
                  goto output_number;

               case 'd':
                  base = 10;
         output_number:
                  int i = va_arg(args, int);
                  // magical code to output 'i' in 'base'. 
                  break;

               default:
                  count++;
                  outputfunc(extra, c);
                  break;
         }
         else
             count++;
             outputfunc(extra, c);
     }
     return count;
 }                

现在，您需要做的就是填入上面的几个位代码并写一个outputfunc（）输出到你的串口。

Now, all you need to do is fill in a few bits of the above code and write an outputfunc() that outputs to your serial port.

注意这是粗略的草图，我确定代码中有一些错误 - 如果你想支持浮点或宽度，你将不得不工作多一点...

Note that this is rough sketch, and I'm sure there are some bugs in the code - and if you want to support floating point or "widths", you will have to work a bit more at it...

（注意额外的参数 - 输出到a FILE * ，这将是文件指针，对于 sprintf ，您可以传递缓冲区的结构，缓冲区，或类似的东西）

(Note on the extra parameter - for output to a FILE * that would be the filepointer, for sprintf, you can pass a structure for the buffer and position in the buffer, or something like that)

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