Debugging Utilities

Because Core Foundation types are opaque, it is difficult to inspect the Core Foundation objects created by your code using traditional means. However, Core Foundation implements a couple of functions that print descriptions of Core Foundation objects, either from your code or in any debugger that supports functions calls.

The first of these functions is CFShow, which takes a reference to any Core Foundation object (that is, its sole parameter is typed as CFTypeRef). This function calls the CFDescription function on the object, causing it to return a reference to a CFString object containing the description. The CFShow function then prints this description to the output device.

The second “inspection” function is CFShowStr, which takes a reference to a CFString object. This function displays the attributes of a CFString object but not its contents.

Listing 1 shows the information printed by both functions in a debugger.

Listing 1  Calling the inspection functions in a debugger

(gdb) s

stringGettingContentsAsCStringExample () at StringExample.c:105

105         str = CFStringCreateWithCString(NULL, "Hello World", CFStringGetSystemEncoding());

(gdb) n

111         bytes = CFStringGetCStringPtr(str, CFStringGetSystemEncoding());

(gdb) call CFShow(str)

Hello World

$1 = 0

(gdb) call CFShowStr(str)

Length 11

IsEightBit 1

HasLengthByte 1

HasNullByte 1

InlineContents 1

Allocator SystemDefault

Mutable 0

Contents 0x4e7c0

$2 = 17

(gdb)