实现自己的变参函数printf

#include <stdarg.h>

void va_start(va_list ap, last);

type va_arg(va_list ap, type);

void va_end(va_list ap);

#include <stdarg.h>

#include <stdio.h>

/*

* Conver int to string based on radix (usually 2, 8, 10, and 16)

*/

char *itoa(int num, char *str, int radix)

{

char  string[] = "0123456789abcdefghijklmnopqrstuvwxyz";

char* ptr = str;

int i;

int j;

while (num)

{

*ptr++  = string[num % radix];

num    /= radix;

if (num < radix)

{

*ptr++  = string[num];

*ptr    = '\0';

break;

}

}

j = ptr - str - 1;

for (i = 0; i < (ptr - str) / 2; i++)

{

int temp = str[i];

str[i]  = str[j];

str[j--] = temp;

}

return str;

}

/*

* A simple printf function. Only support the following format:

*          Code            Format

*          %c              character

*          %d              signed integers

*          %i              signed integers

*          %s              a string of characters

*          %o              octal

*          %x              unsigned hexadecimal

*/

int my_printf( const char* format, ...)

{

va_list arg;

int done = 0;

va_start (arg, format);

//done = vfprintf (stdout, format, arg);

while( *format != '\0')

{

if( *format == '%')

{

if( *(format+1) == 'c' )

{

char c = (char)va_arg(arg, int);

putc(c, stdout);

} else if( *(format+1) == 'd'  || *(format+1) == 'i')

{

char store[20];

int i = va_arg(arg, int);

char* str = store;

itoa(i, store, 10);

while( *str != '\0') putc(*str++, stdout);

} else if( *(format+1) == 'o')

{

char store[20];

int i = va_arg(arg, int);

char* str = store;

itoa(i, store, 8);

while( *str != '\0') putc(*str++, stdout);

} else if(  *(format+1) == 'x')

{

char store[20];

int i = va_arg(arg, int);

char* str = store;

itoa(i, store, 16);

while( *str != '\0') putc(*str++, stdout);

} else if( *(format+1) == 's' )

{

char* str = va_arg(arg, char*);

while( *str != '\0') putc(*str++, stdout);

}

// Skip this two characters.

format += 2;

} else {

putc(*format++, stdout);

}

}

va_end (arg);

return done;

}

int main(int argc, char* argv[])

{

int n = 255;

char str[] = "hello, world!";

printf("n = %d\n", n);

printf("n = %i\n", n);

printf("n = %o\n", n);

printf("n = %x\n", n);

printf("first char = %c\n", str[0]);

printf("str = %s\n", str);

printf("%s\tn = %d\n", str, n);

// Test my_printf function

printf("---------------my_printf--------------\n");

my_printf("n = %d\n", n);

my_printf("n = %i\n", n);

my_printf("n = %o\n", n);

my_printf("n = %x\n", n);

my_printf("first char = %c\n", str[0]);

my_printf("str = %s\n", str);

my_printf("%s\tn = %d\n", str, n);

return 0;

}