mmoss@csws9.ic.sunysb.edu (Matthew D Moss) (01/28/91)
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? And, if I were to use char*, do I have to allocate space before I define the string? (Sorry if this has been asked before :) Thanks, Matthew Moss (mmoss@libserv1.ic.sunysb.edu)
hairston@henry.ECE.CMU.EDU (David Hairston) (01/28/91)
[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
Lawson.English@p88.f15.n300.z1.fidonet.org (Lawson English) (02/01/91)
Matthew D Moss writes in a message to All
MDM> Can someone tell me what exactly is the difference between Str255
MDM> and char*
"char*" is a pointer to an arbitrary number of bytes. Str255 is an array of
256 bytes with a length byte at the beginning (hence Str255). You can use a
Str255 as a char* with typecasting, but you must remember to begin the reference
to the char-data at myStr255[1]: "*((char *)myStr255+1)" or somesuch (allowing
for bad parenthesis usage).
Lawson
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