printf function Source Code implementation

#include  <stdio.h> #include  <stdarg.h>//va_start (Arg,format), initialize the parameter pointer arg, Assigning the first parameter address to the right of the function parameter to Arg//format must be a pointer to a parameter, so that the type function should have at least one common parameter,  //thereby providing to va_start  Va_ Start to find the position of the mutable parameter on the stack.  //va_arg (Arg,char), gets the value of arg pointing to the parameter, while Arg refers to the next argument, char is used to nominate the current parameter type//va_end  in some implementations may change arg to an invalid value, here, the ARG pointer is pointed to the  null, avoid the presence of wild hands  void print (const char *format,  ...) {Va_list arg;va_start (Arg, format);while  (*format) {char ret = *format;if  ( ret ==  '% ') {switch  (*++format) {case  ' C ': {Char ch = va_arg (Arg, char); Putchar (ch); break;} case  ' s ': {char *pc = va_arg (arg, char *);while  (*pc) {Putchar (*pc);p C + +;} break;} Default:break;}} Else{putchar (*format);} format++;} Va_end (ARG);} Int main () {print ("%s %s %c%c%c%c%c!\n",  "Welcome",  "to",  ' C ',  ' h ',  ' I ' ,  ' n ',  ' a '); System ("pause"); return 0;}

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printf function Source Code implementation