Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!rochester!pt.cs.cmu.edu!henry.ECE.CMU.EDU!hairston
From: hairston@henry.ECE.CMU.EDU (David Hairston)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Str255 and char*
Keywords: THINK C 4.0
Message-ID: <11689@pt.cs.cmu.edu>
Date: 27 Jan 91 20:35:17 GMT
References: <1991Jan27.181816.22644@sbcs.sunysb.edu>
Distribution: usa
Organization: Gaia II
Lines: 50

[mmoss@csws9.ic.sunysb.edu (Matthew D Moss) writes:]
[] Can someone tell me what exactly is the difference between
[] >Str255 and char* ?
[]
[] Looking through source files, I see Str255 defined as an
[] array. Is that the same as a char pointer?

the type definition of Str255 in the THINK C enviroment is:
typedef unsigned char Str255[256];

makes sense considering the length byte which preceeds pascal
strings.

when using Str255's in situations that require (char *)'s you
need to make a cast because of the difference in underlying
type (char vs unsigned char) and consider the syntax of the
string (i.e. a pascal string is preceded by an unsigned length
byte and a c string is terminated by a null byte).  there are
tools for handling these conversions.

Str255 is defined as an array which does allocate storage
(i.e. 256 unsigned chars at a fixed address).  a pointer does
not allocate storage for the object pointed at, just storage
for itself (i.e. a long word).

[] And, if I were to use char*, do I have to allocate space
[] before I define the string?

depends ... ;)

char *cp = "address of string constant";

is okay if you simply want to use a fixed string.

the following is also okay (i haven't considered pascal <=> c issues):

int  some_flag;
char cbuf1[256], cbuf2[256], *cp;

...
strcpy(cbuf1, "a given string value");
strcpy(cbuf2, "another string value");
cp = (some_flag ? cbuf1 : cbuf2);

in this case, changing the pointer doesn't lose information as it
would in the first example.  there are other reasons for using
buffers (arrays) also.

  -dave-  
hairston@henry.ece.cmu.edu