Developing Series 60 Applications: A Guide for Symbian OS C++ Developers: A Guide for Symbian OS C++ Developers

The basic types used throughout Symbian OS are shown in Table 3-1. They are mainly defined in the system include file e32defs.h (which is often #include d implicitly, as part of e32base.h ), and they all have a T -class interface, so they do not require complex construction or explicit destructors. Many of them are actually implemented as compiler-specific typedef s of standard C++ types, providing guaranteed platform independence. Some are implemented as actual simple C++ classes. Note that the Symbian OS types should always be used in preference to built-in C++ types. For example, you should always use TInt instead of int .

Note that the implementation of TBool seems very wasteful , considering that 32 bits are used to store one of two possible values. There are several reasons for this, including:

• Ease of passing as an argument, since individual bits cannot be passed.

• Lack of ratified native boolean type when Symbian OS was developed.

• Necessity of a direct mapping onto int for use in conditional expressions.

However, note that you should never compare a TBool directly to Etrue , as any nonzero value is also considered "true." For example:

TInt b = 2; if (b == ETrue) { // This statement is "false"! } if (b) // Will return "true" as required. { // Use this form instead. }

Similarly, you should not compare TBool values to EFalse ”even though the code will work, it is inefficient and inconsistent. Instead use the following form:

if (!b) { // b is "false". }

If your class uses a lot of Boolean attributes, and if minimum memory usage is a goal, then you might consider using bit packing. However, this is beyond the scope of this book.

Table 3-1. The Basic Types in Symbian OS