diff -r 000000000000 -r 89d6a7a84779 Symbian3/SDK/Source/GUID-4C1F3DB3-039C-57D6-987F-4A26E1E056E6.dita --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/Symbian3/SDK/Source/GUID-4C1F3DB3-039C-57D6-987F-4A26E1E056E6.dita Thu Jan 21 18:18:20 2010 +0000 @@ -0,0 +1,85 @@ + + + + + +How to use the non-modifiable pointer descriptor - TPtrCNon-modifiable pointer descriptors are useful for referencing + constant strings or data; for example, accessing strings built into ROM + resident code, or passing a reference to data in RAM which must not be modified + through that reference. +
+ Constructing a <codeph>TPtrC</codeph> +

A non-modifiable pointer descriptor can be constructed in a number + of ways:

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    any other descriptor.

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    another non-modifiable pointer descriptor.

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    a pointer into memory and specifying the length of the + data.

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    a zero terminated string.

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+

The following code fragment constructs a TPtrC to + represent the data already represented by any other type of descriptor.

+

The source descriptor is a literal which is converted to descriptor + type.

+ _LIT(KText,"Hello World!"); +... +TBufC<16> buf1(KText); // buf1 is the existing descriptor +... +TPtrC ptr(buf1); // data in buf1 now accessible through ptr +

The following code fragment constructs a TPtrC to + represent the data already represented by another TPtrC.

+ _LIT(KText,"Hello World!"); +... +TBufC<16> buf1(KText); // buf1 is the existing descriptor +... +TPtrC ptr1(buf1); // data in buf1 now accessible through ptr1 +TPtrC ptr2(ptr1); // data also accessible through ptr2 +

Although rarely used (possibly in porting legacy 'C' code), the + following code fragment defines a constant C style non-Unicode + string and then constructs the non-modifiable pointer descriptor for that + string. The explicit 8 bit variant is used here. The descriptor is separate + from the data it represents.

+ const TText8* cstr = (TText8*)"Hello World!"; +... +TPtrC8 ptr(cstr); +... +ptr.Length(); // The length is 12. +ptr.Ptr(); // The address of the descriptor's data, + // i.e. 'C' string. +

The following code fragment shows construction from a pointer into + memory and a length. The example assumes that both the pointer and the length + have valid values:

+ TUint8* memptr; +TInt length; +... +TPtrC8 ptr(memptr,length);
+
+Accessing data

Once a +non-modifiable pointer descriptor has been constructed, the functions in the +base class, TDesC, are available to access the +data.

For example, given a pointer descriptor labelled ptr:#

_LIT(KText,"Hello World!"); +... +TBufC<16> buf1(KText); // buf1 is the existing descriptor +... +TPtrC ptr(buf1); // data in buf1 now accessible through ptr +... +ptr.Length(); // returns the length of the data (i.e. 12) + + +
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