Creating Functions that use Format control Strings

This is a discussion on Creating Functions that use Format control Strings within the C Programming forums, part of the General Programming Boards category; Is it possible to create functions that are similar to scanf in the sense that I can use a format ...

  1. #1
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    Creating Functions that use Format control Strings

    Is it possible to create functions that are similar to scanf in the sense that I can use a format control string to determine how many variables the function will take in?

    eg:
    new_function(const char*, var1, var2, var3,...);

    if so, can anyone point me in the direction of where to look for more information regarding this?
    (Or can anyone tell me where I can sneak a peek at the scanf functions to see how they work...)

  2. #2
    Registered User hk_mp5kpdw's Avatar
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    Quote Originally Posted by tzuchan
    Is it possible to create functions that are similar to scanf in the sense that I can use a format control string to determine how many variables the function will take in?

    eg:
    new_function(const char*, var1, var2, var3,...);

    if so, can anyone point me in the direction of where to look for more information regarding this?
    (Or can anyone tell me where I can sneak a peek at the scanf functions to see how they work...)
    Functions using variable numbers of parameters can be coded using the va_start, va_end, and va_arg functions that are declared in the stdio.h header.
    "Owners of dogs will have noticed that, if you provide them with food and water and shelter and affection, they will think you are god. Whereas owners of cats are compelled to realize that, if you provide them with food and water and shelter and affection, they draw the conclusion that they are gods."
    -Christopher Hitchens

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    Obsessed with C chrismiceli's Avatar
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    Quote Originally Posted by hk_mp5kpdw
    Functions using variable numbers of parameters can be coded using the va_start, va_end, and va_arg functions that are declared in the stdio.h header.
    Err... Just looked through my stdio.h file...
    Didn't find any of those functions...
    I'm using the mingw32 compiler... Any ideas where else I should try looking?

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    Quote Originally Posted by chrismiceli
    Whee! just what I was looking for, thanks!

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    Registered User hk_mp5kpdw's Avatar
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    Quote Originally Posted by tzuchan
    Err... Just looked through my stdio.h file...
    Didn't find any of those functions...
    I'm using the mingw32 compiler... Any ideas where else I should try looking?
    Oops, sorry bout that. The required header appear to be stdarg.h or optionally varargs.h.
    "Owners of dogs will have noticed that, if you provide them with food and water and shelter and affection, they will think you are god. Whereas owners of cats are compelled to realize that, if you provide them with food and water and shelter and affection, they draw the conclusion that they are gods."
    -Christopher Hitchens

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    Guest Sebastiani's Avatar
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    This doesn't really do much, but it's a start, anyway:

    Code:
     int sprint(char buffer[], const char * first, ...)
    { 
     const char * fmt = first;
     
     char * b = buffer;
     
     char ch;
     
     va_list vap;
     
     va_start(vap, first);
      
         while(*fmt)
        {
         ch = *fmt++;
         
             if(ch == '%')
            {     
             ch = *fmt++;
                     
                 if(ch == 's')
                {             
                 char * vs = va_arg(vap, char*);
    
                     while(*vs)
                    {
                     *b++ = *vs++;
                    }
                }    
                 else // ...not recognized...
                {
                 --fmt;
                }          
            }
             else // ... just copy...
            {
             *b++ = ch;
            }     
        } 
     
     *b = 0;
     
     va_end(vap);
     
     return b - buffer;
    }
    Code:
    #include <cmath>
    #include <complex>
    bool euler_flip(bool value)
    {
        return std::pow
        (
            std::complex<float>(std::exp(1.0)), 
            std::complex<float>(0, 1) 
            * std::complex<float>(std::atan(1.0)
            *(1 << (value + 2)))
        ).real() < 0;
    }

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