[plt-scheme] problem with string

besson baptiste wrote:

> This is suppose to  cast val into a string padded to
> the length of exp.
> for ex:
> (str$ 176 4) should return \0176
> instead I always get two zero 00 before val
> 
>>(str$ 176 4)
> 
> "\000176"
> 
> but I get
> 
> 
>>(string-length (str$ 176 4))
> 
> 4
> 
> which is what I want.
> I don't understand why is these 00  appear for any
> value of val and exp.

Chapter 14 of the PLT MzScheme: Language Manual has the following:

Within string constants, the following escape sequences are recognized in addition to \" and \\:

* \a: alarm (ASCII 7)

* \b: backspace (ASCII 8)

* \t: tab (ASCII 9)

* \n: linefeed (ASCII 10)

* \v: vertical tab (ASCII 11)

* \f: formfeed (ASCII 12)

* \r: return (ASCII 13)

* \e: escape (ASCII 27)

* \o, \oo, or \ooo: ASCII for octal o, oo, or ooo, where each o is 0, 1, 2, 3, 4, 5, 6, or 7. The \ooo form takes 
precedence over the \oo form, and \oo takes precedence over \o.

* \xh or \xhh: ASCII for hexadecimal h or hh, where each h is 0, 1, 2, 3, 4, 5, 6, 7, a, A, b, B, c, C, d, D, e, E, f, 
or F. The \xhh form takes precedence over the \xh form.

Furthermore, a backslash followed by a linefeed, carriage return or return-linefeed combination is elided, allowing 
string constants to span lines. Any other use of backslash within a string constant is an error.


The import one here is the \ooo which means that \000 is parsed as the char with the ascii-number 0.
I.e. the external syntax \000 represent one char.

-- 
Jens Axel Søgaard