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Full Discussion: Problem with function which reutrns pointer to a value
Top Forums Programming Problem with function which reutrns pointer to a value Post 87845 by mbb on Friday 28th of October 2005 10:03:00 AM
Old 10-28-2005
Your other post implies you may be passing back a string.

You may prefer to use strcpy like so:

char CountryName[XX*];

strcpy(CountryName, pcCityIdToCountryName(..................) );

*where XX is the size of the string.

The reason being is that you don't know if the char pointer being passed back is still pointing to an allocated memory block. Sometimes I have seen functions pass back a pointer to a local variable or memory being allocated and then made free. It just so happens that you are pointing to a memory location that still has a string (null terminated) value. This may not be the case later on in the program's execution, especially when you are allocating and freeing memory frequently, and you may encounter a memory violation.

At least by copying string into a local variable you can protect against any future problems.

Of course, if it is your own function, you can make your own judgements as to the best way to call it, based on your overall design.
 

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LEARN ABOUT DEBIAN

xtnew

XtMalloc(3)							   XT FUNCTIONS 						       XtMalloc(3)

NAME

       XtMalloc, XtCalloc, XtRealloc, XtFree, XtNew, XtNewString - memory management functions

SYNTAX

       char *XtMalloc(Cardinal size);

       char *XtCalloc(Cardinal num, Cardinal size);

       char *XtRealloc(char *ptr, Cardinal num);

       void XtFree(char *ptr);

       type *XtNew(type);

       String XtNewString(String string);

       Cardinal XtAsprintf(String *new_string, const char *format, ...);

ARGUMENTS

       num	 Specifies the number of bytes or array elements.

       ptr	 Specifies a pointer to the old storage or to the block of storage that is to be freed.

       size	 Specifies the size of an array element (in bytes) or the number of bytes desired.

       string	 Specifies a previously declared string.

       type	 Specifies a previously declared data type.

       new_string
		 Specifies a pointer to write a newly allocated string to.

       format	 Specifies a formatting string as defined by sprintf(3c)

DESCRIPTION

       The XtMalloc functions returns a pointer to a block of storage of at least the specified size bytes.  If there is insufficient memory to
       allocate the new block, XtMalloc calls XtErrorMsg.

       The XtCalloc function allocates space for the specified number of array elements of the specified size and initializes the space to zero.
       If there is insufficient memory to allocate the new block, XtCalloc calls XtErrorMsg.

       The XtRealloc function changes the size of a block of storage (possibly moving it).  Then, it copies the old contents (or as much as will
       fit) into the new block and frees the old block.  If there is insufficient memory to allocate the new block, XtRealloc calls XtErrorMsg.
       If ptr is NULL, XtRealloc allocates the new storage without copying the old contents; that is, it simply calls XtMalloc.

       The XtFree function returns storage and allows it to be reused.	If ptr is NULL, XtFree returns immediately.

       XtNew returns a pointer to the allocated storage.  If there is insufficient memory to allocate the new block, XtNew calls XtErrorMsg.
       XtNew is a convenience macro that calls XtMalloc with the following arguments specified:

       ((type *) XtMalloc((unsigned) sizeof(type))

       XtNewString returns a pointer to the allocated storage.	If there is insufficient memory to allocate the new block, XtNewString calls XtEr-
       rorMsg.	XtNewString is a convenience macro that calls XtMalloc with the following arguments specified:

       (strcpy(XtMalloc((unsigned) strlen(str) + 1), str))

       The XtAsprintf function allocates space for a string large enough to hold the string specified by the sprintf(3c) format pattern when used
       with the remaining arguments, and fills it with the formatted results.  The address of the allocated string is placed into the pointer
       passed as ret.  The length of the string (not including the terminating null byte) is returned.	If there is insufficient memory to allo-
       cate the new block, XtAsprintf calls XtErrorMsg.

SEE ALSO

       X Toolkit Intrinsics - C Language Interface
       Xlib - C Language X Interface

X Version 11							    libXt 1.1.3 						       XtMalloc(3)
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