Buffer -descriptors

A buffer descriptor provides a fixed length buffer to contain and access -data. The data is part of the descriptor object.

A buffer descriptor object is an instance of a templated class, where the -template parameter is an integer value that defines the size of the descriptor's -data area.

A buffer descriptor comes in two forms:

a non-modifiable buffer -descriptor.
a modifiable buffer -descriptor.

Non-modifiable buffer descriptor

The data contained -in a non-modifiable buffer descriptor can be accessed, but not changed, through -this descriptor. The data can, however, be completely replaced using the assignment -operators.

Data is accessed through functions provided by the base -class.

A non-modifiable buffer descriptor is supplied in two variants:

the 16 bit variant, -a TBufC16<TInt>, to contain Unicode strings.
the 8 bit variant, a TBufC8<TInt>, -to contain non-Unicode strings and binary data.

There is also a build independent type, TBufC<TInt>. -This is the type which is most commonly used in program code; the appropriate -variant is selected at build time.

An explicit 8 bit variant is chosen -for binary data. The explicit 16 bit variant is rarely used.

The base -class, TDesC, contains a data member which holds the length -of the data. The following drawing shows the layout of a TBufC<5> object -initialised with the string of five characters representing the English word -"Hello".

- -

Modifiable buffer descriptor

The data contained -in a modifiable buffer descriptor can be both accessed and changed through -this descriptor.

The template parameter, as well as determining the -size of the data area created as part of the descriptor object, also defines -the maximum length of the descriptor.

The length of the data can vary -between zero and the maximum length. When the length of the data is less than -the maximum, a portion of the data area within the descriptor is unused.

Data -is accessed and modified through functions provided by the base classes.

A -modifiable buffer descriptor is supplied in two variants:

the 16 bit variant, -a TBuf16<TInt>, to contain Unicode strings.
the 8 bit variant, a TBuf8<TInt>, -to contain non-Unicode strings and binary data.

There is also a build independent type, TBuf<TInt>. -This is the type which is most commonly used in program code; the appropriate -variant is selected at build time.

An explicit 8 bit variant is chosen -for binary data. The explicit 16 bit variant is rarely used.

The base -class TDesC, contains a data member that holds the length -of the data. The base class TDes, contains a data member -that holds the maximum length of the data. The following drawing shows the -layout of a TBuf<12> object initialised with the string -of five characters representing the English word "Hello".

- -

+ + + + + +Buffer +descriptorsDescribes modifiable and non-modifiable buffer descriptors. +

A buffer descriptor provides a fixed length buffer to contain and access +data. The data is part of the descriptor object.

A buffer descriptor object is an instance of a templated class, where the +template parameter is an integer value that defines the size of the descriptor's +data area.

A buffer descriptor comes in two forms:

a non-modifiable buffer +descriptor.
a modifiable buffer +descriptor.

Non-modifiable buffer descriptor

The data contained +in a non-modifiable buffer descriptor can be accessed, but not changed, through +this descriptor. The data can, however, be completely replaced using the assignment +operators.

Data is accessed through functions provided by the base +class.

A non-modifiable buffer descriptor is supplied in two variants:

the 16 bit variant, +a TBufC16<TInt>, to contain Unicode strings.
the 8 bit variant, a TBufC8<TInt>, +to contain non-Unicode strings and binary data.

There is also a build independent type, TBufC<TInt>. +This is the type which is most commonly used in program code; the appropriate +variant is selected at build time.

An explicit 8 bit variant is chosen +for binary data. The explicit 16 bit variant is rarely used.

The base +class, TDesC, contains a data member which holds the length +of the data. The following drawing shows the layout of a TBufC<5> object +initialised with the string of five characters representing the English word +"Hello".

+ +

Modifiable buffer descriptor

The data contained +in a modifiable buffer descriptor can be both accessed and changed through +this descriptor.

The template parameter, as well as determining the +size of the data area created as part of the descriptor object, also defines +the maximum length of the descriptor.

The length of the data can vary +between zero and the maximum length. When the length of the data is less than +the maximum, a portion of the data area within the descriptor is unused.

Data +is accessed and modified through functions provided by the base classes.

A +modifiable buffer descriptor is supplied in two variants:

the 16 bit variant, +a TBuf16<TInt>, to contain Unicode strings.
the 8 bit variant, a TBuf8<TInt>, +to contain non-Unicode strings and binary data.

There is also a build independent type, TBuf<TInt>. +This is the type which is most commonly used in program code; the appropriate +variant is selected at build time.

An explicit 8 bit variant is chosen +for binary data. The explicit 16 bit variant is rarely used.

The base +class TDesC, contains a data member that holds the length +of the data. The base class TDes, contains a data member +that holds the maximum length of the data. The following drawing shows the +layout of a TBuf<12> object initialised with the string +of five characters representing the English word "Hello".

+ +

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