How to -use modifiable buffer descriptor

How to -use modifiable buffer descriptor — TBuf<TInt>Modifiable buffer descriptors are useful for holding strings or -data and providing safe ways to access and modify that data. -

For text data, it is -usual to construct a TBuf<TInt> type and allow the appropriate -variant, either a TBuf8<TInt> or a TBuf16<TInt> to -be selected at build time.
For binary data, an -explicit TBuf8<TInt> is used.
It is rare to use an -explicit TBuf16<TInt>.

Although, the following notes refer to the build independent types; they -are equally valid for the explicit 8 bit and 16 bit types.

Constructing -a TBuf<TInt>

A modifiable buffer descriptor can be constructed -in a number of ways:

as an empty buffer descriptor.
as an empty buffer descriptor -but giving it a length.
by copying data from -any other type of descriptor.
by copying data from -another modifiable buffer descriptor of the same size.

The following code fragment constructs a TBuf<16> object. -The buffer descriptor is uninitialised, i.e. it contains no data. The assignment -operator or the Copy() function can be used to put data into -the buffer descriptor after construction:

_LIT(KText,"Hello World!"); -... -TBuf<16> buf1; // length of buf1 is 0 -... -buf1 = KText; // data assigned

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

The following code fragment -constructs a TBuf<16> object and sets it length to 12. -No data is assigned into the descriptor.

... -TBuf<16> buf1(12); // length of buf1 is 12 -...

The following code fragment constructs a TBuf<16> object, -initialised with the 12 characters making up the English language phrase "Hello -World!".

_LIT(KText,"Hello World!"); -... -TBuf<16> buf1(KText);

The following code fragment constructs -a TBuf<16> object from another TBuf<16> object. -This is, in effect, copy construction.

_LIT(KText,"Hello World!"); -... -TBuf<16> buf1(KText); -TBuf<16> buf2(buf1); // buf2 constructed from the data in buf1

In -both of these cases, the resulting length of the descriptor is 12.

A -non-modifiable buffer descriptor can also be constructed from 'C' style zero -terminated string. However, this is rarely necessary but may make it easier -to port legacy 'C' code.

Replacing data

Data -within a modifiable buffer descriptor can be completely replaced through the -assignment operator or by using the Copy() function.

_LIT(KText,"Hello World!"); -_LIT(KNewText,"New text"); -_LIT(KReplaced,"Replaced"); -... -TBuf<16> buf1(KText); -TBuf<16> buf2; -... -buf2 = buf1; // buf2 now contains "Hello World!" -... -buf2 = KNewText; // buf2 now contains "New text". - // the literal is converted to a descriptor - // type. -buf2.Copy(KReplaced); // buf2 content replaced using Copy()

Accessing and -changing data

Once a modifiable buffer descriptor has been constructed, -the functions in the base classes, TDesC and TDes, -are available to be access and change the data.

_LIT(KText,"Hello World!"); -... -TBufC<16> buf1(KText); -... -buf1.Length();

and

_LIT(KText,"Hello World!"); -... -TBufC<16> buf1(KText); // length is 12 -... -buf1.Delete(6,6); // length is now 6, leaving "Hello" in - // the buffer

Illegal access -causing an exception

The following code fragment raises a panic -because of an attempt to assign too much data. The maximum length of the buffer -descriptor is 16 but the length of the data to be copied is 31:

_LIT(KText,"Hello World! The sun is shining"); -... -TBufC<16> buf1(KText);

The following code fragment raises -a panic because of an attempt to delete data outside the boundary defined -by the descriptor:

_LIT(KText,"Hello World!"); -... -TBufC<16> buf1(KText); -buf1.Delete(99,1);

- -Literal Descriptors - + + + + + +How to use modifiable buffer descriptor — TBuf<TInt>Modifiable buffer descriptors are useful for holding strings +or data and providing safe ways to access and modify that data. +

For text data, +it is usual to construct a TBuf<TInt> type and +allow the appropriate variant, either a TBuf8<TInt> or a TBuf16<TInt> to be selected at build time.
For binary data, +an explicit TBuf8<TInt> is used.
It is rare to +use an explicit TBuf16<TInt>.

Although, the following notes refer to the build independent types; +they are equally valid for the explicit 8 bit and 16 bit types.

Constructing +a TBuf<TInt>

A modifiable buffer descriptor can be constructed +in a number of ways:

as an empty +buffer descriptor.
as an empty +buffer descriptor but giving it a length.
by copying data +from any other type of descriptor.
by copying data +from another modifiable buffer descriptor of the same size.

The following code fragment constructs a TBuf<16> object. The buffer descriptor is uninitialised, i.e. it contains +no data. The assignment operator or the Copy() function +can be used to put data into the buffer descriptor after construction:

_LIT(KText,"Hello World!"); +... +TBuf<16> buf1; // length of buf1 is 0 +... +buf1 = KText; // data assigned

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

The following +code fragment constructs a TBuf<16> object and +sets it length to 12. No data is assigned into the descriptor.

... +TBuf<16> buf1(12); // length of buf1 is 12 +...

The following code fragment constructs a TBuf<16> object, initialised with the 12 characters making +up the English language phrase "Hello World!".

_LIT(KText,"Hello World!"); +... +TBuf<16> buf1(KText);

The following code fragment +constructs a TBuf<16> object from another TBuf<16> object. This is, in effect, copy construction.

_LIT(KText,"Hello World!"); +... +TBuf<16> buf1(KText); +TBuf<16> buf2(buf1); // buf2 constructed from the data in buf1

In both of these cases, the resulting length of the descriptor +is 12.

A non-modifiable buffer descriptor can also be constructed +from 'C' style zero terminated string. However, this is rarely necessary +but may make it easier to port legacy 'C' code.

Replacing +data

Data within a modifiable buffer descriptor can be +completely replaced through the assignment operator or by using the Copy() function.

_LIT(KText,"Hello World!"); +_LIT(KNewText,"New text"); +_LIT(KReplaced,"Replaced"); +... +TBuf<16> buf1(KText); +TBuf<16> buf2; +... +buf2 = buf1; // buf2 now contains "Hello World!" +... +buf2 = KNewText; // buf2 now contains "New text". + // the literal is converted to a descriptor + // type. +buf2.Copy(KReplaced); // buf2 content replaced using Copy()

Accessing +and changing data

Once a modifiable buffer descriptor has +been constructed, the functions in the base classes, TDesC and TDes, are available to be access and change +the data.

_LIT(KText,"Hello World!"); +... +TBufC<16> buf1(KText); +... +buf1.Length();

and

_LIT(KText,"Hello World!"); +... +TBufC<16> buf1(KText); // length is 12 +... +buf1.Delete(6,6); // length is now 6, leaving "Hello" in + // the buffer

Illegal +access causing an exception

The following code fragment +raises a panic because of an attempt to assign too much data. The +maximum length of the buffer descriptor is 16 but the length of the +data to be copied is 31:

_LIT(KText,"Hello World! The sun is shining"); +... +TBufC<16> buf1(KText);

The following code fragment +raises a panic because of an attempt to delete data outside the boundary +defined by the descriptor:

_LIT(KText,"Hello World!"); +... +TBufC<16> buf1(KText); +buf1.Delete(99,1);

+ +Literal Descriptors

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