[C] printf library function

  The printf function implemented in this article is declared as:

void VarPrint(const char * format, ...);

  It mainly realizes the printing of strings, characters and numbers (ps: positive and negative numbers and 0). Of course, this is only a part of the function. Subsequent versions will support printing in multiple formats, so stay tuned.

Analysis of Algorithms

  Starting from the content to be printed, each time judge whether a character is '%', if it is not '%', then output as it is (putchar can be used), if it is '%', then judge the character after '%' It is s, or c, or d, and finally print the output according to the format.

  Note: Remember not to use puts when printing strings, because puts will automatically wrap the line after printing the statement to be output.

Source code:

#define _CRT_SECURE_NO_WARNINGS 1

/*
* Copyright (c) 2018, code farmer from sust
* All rights reserved.
*
* File name: VarPrint.c
* Function: simulate the implementation of the printf function
* Support output in %s, %c, %d and other formats
*
* Current version: V1.0
* Author: sustzc
* Completion date: April 20, 2018 11:12:26
*/

# include <stdio.h>
# include <assert.h>
# include <stdarg.h>

/*
* Function name: PrintStr
*
* Function: print string
*
* Entry parameter: str
*
* Exit parameter: void
*
* Return type: void
*/

void PrintStr(char * str)
{
	assert(NULL != str);

	while ('\0' != *str)
	{
		putchar(*str++);
	}

	return;
}

/*
* Function name: PrintInt
*
* Function: print numbers
*
* Entry parameter: num
*
* Exit parameter: void
*
* Return type: void
*/

void PrintInt(int num)
{
	if (num >= 0)
	{
		if (num > 9)
		{
			PrintInt(num / 10);
		}
		else
		{
			;
		}

		putchar(num % 10 + '0');
	}
	else
	{
		putchar('-');

		if ((-num) > 9)
		{
			PrintInt((-num) / 10);
		}
		else
		{
			;
		}

		putchar((-num)%10 + '0');
	}

	return;
}

/*
* Function name: VarPrint
*
* Function function: implement the printf function
*
* Entry parameters: format, ...
*
* Exit parameter: void
*
* Return type: void
*/

void VarPrint(const char * format, ...)
{
	va_list arg;
	int i = 0;
	int count = 0;

	assert(NULL != format);
	va_start (arg, format);

	while ('\0' != *format)
	{
		if ('%' == *format)
		{
			switch(*(++format))
			{
				case 's':
					PrintStr (va_arg (arg, char *));
					break;
				case 'c':
					putchar (va_arg (arg, unsigned int));
					break;
				case 'd':
					PrintInt (va_arg (arg, int));
					break;
				default:
					break;
			}

			format++;
		}
		else
		{
			putchar(*format++);
		}
	}

	va_end (arg);

	return;
}

int main(void)
{
	VarPrint("printstr: %s\n", "h e l l o");
	VarPrint("printchar: %c\n", 'c');
	VarPrint("printchar: %c\n", 'h');
	VarPrint("printchar: %c\n", 'i');
	VarPrint("printchar: %c\n", 'n');
	VarPrint("printchar: %c\n", 'a');
	VarPrint("printint: %d\n", -520);
	VarPrint("printint: %d\n", 1314);
		
	return 0;
}

Output result: