NSPR Types (Chapter 2)
This chapter describes the most common NSPR types. Other chapters describe more specialized types when describing the functions that use them.
- Calling Convention Types are used for externally visible functions and globals.
- Algebraic Types of various lengths are used for integer algebra.
- Miscellaneous Types are used for representing size, pointer difference, Boolean values, and return values.
For information on naming conventions for NSPR types, functions, and macros, see NSPR Naming Conventions.
Calling Convention Types
These types are used to support cross-platform declarations of prototypes and implementations:
PR_EXTERNis used for definitions of external functions or variables.PR_IMPLEMENTis used for declarations of external functions or variables.PR_CALLBACKis used for definitions and declarations of functions that are called via function pointers. A typical example is a function implemented in an application but called from a shared library.
Here are some simple examples of the use of these types:
In dowhim.h:
PR_EXTERN( void ) DoWhatIMean( void );
static void PR_CALLBACK RootFunction(void *arg);
In dowhim.c:
PR_IMPLEMENT( void ) DoWhatIMean( void ) { return; };
PRThread *thread = PR_CreateThread(..., RootFunction, ...);
PR_EXTERN
Used to define the prototypes for functions or variables that are to be exported from a shared library.
Syntax
#include <prtypes.h>
PR_EXTERN(type) prototype
Description
PR_EXTERN is used to define externally visible routines and globals. For syntax
details for each platform, see prtypes.h. The macro includes the proper
specifications to declare the target extern and set up other required linkages.
Warning
Some platforms do not allow the use of the underscore character (_) as the first
character of an exported symbol.
PR_IMPLEMENT
Used to define implementations of symbols that are to be exported from a shared library.
Syntax
#include <prtypes.h>
PR_IMPLEMENTtype) implementation
Description
PR_IMPLEMENT is used to define implementations of externally visible routines and
globals. For syntax details for each platform, see prtypes.h.
Warning
Some platforms do not allow the use of the underscore character (_) as the first
character of an exported symbol.
PR_CALLBACK
Used to define pointers to functions that will be implemented by the client but called from a (different) shared library.
Syntax
#include <prtypes.h>
type PR_CALLBACK implementation
Description
Functions that are implemented in an application (or shared library) that are
intended to be called from another shared library (such as NSPR) must be declared
with the PR_CALLBACK attribute. Normally such functions are passed by reference
(pointer to function). The PR_CALLBACK attribute is included as part of the
function's definition between its return value type and the function's name.
Algebraic Types
NSPR provides the following type definitions with unambiguous bit widths for algebraic operations:
For convenience, NSPR also provides type definitions with platform-dependent bit widths:
8-, 16-, and 32-bit Integer Types
Signed Integers
PRInt8
Guaranteed to be a signed 8-bit integer on all platforms.
Syntax
#include <prtypes.h>
typedef definition PRInt8;
PRInt16
Guaranteed to be a signed 16-bit integer on all platforms.
Syntax
#include <prtypes.h>
typedef definition PRInt16;
PRInt32
Guaranteed to be a signed 32-bit integer on all platforms.
Syntax
#include <prtypes.h>
typedef definition PRInt32;
Description
May be defined as an int or a long, depending on the platform. For syntax details
for each platform, see prtypes.h.
Unsigned Integers
PRUint8
Guaranteed to be an unsigned 8-bit integer on all platforms. There is no type
equivalent to a plain char.
Syntax
#include <prtypes.h>
typedef definition PRUint8;
PRUint16
Guaranteed to be an unsigned 16-bit integer on all platforms.
Syntax
#include <prtypes.h>
typedef definition PRUint16;
PRUint32
Guaranteed to be an unsigned 32-bit integer on all platforms.
#include <prtypes.h>
typedef definition PRUint32;
Description
May be defined as an unsigned int or an unsigned long, depending on the
platform. For syntax details for each platform, see prtypes.h.
64-bit Integer Types
Different platforms treat 64-bit numeric fields in different ways. Some systems
require emulation of 64-bit fields by using two 32-bit numeric fields bound in a
structure. Since the types (long long versus struct LONGLONG) are not type
compatible, NSPR defines macros to manipulate 64-bit numeric fields. These
macros are defined in prlong.h. Conscientious use of these macros ensures
portability of code to all the platforms supported by NSPR and still provides
optimal behavior on those systems that treat long long values directly.
PRInt64
Guaranteed to be a signed 64-bit integer on all platforms.
Syntax
#include <prtypes.h>
typedef definition PRInt64;
Description
May be defined in several different ways, depending on the platform. For syntax
details for each platform, see prtypes.h.
PRUint64
Guaranteed to be an unsigned 64-bit integer on all platforms.
Syntax
#include <prtypes.h>
typedef definition PRUint64;
Description
May be defined in several different ways, depending on the platform. For syntax
details for each platform, see prtypes.h.
Floating-Point Number Type
The NSPR floating-point type is always 64 bits.
Syntax
#include <prtypes.h>
typedef double PRFloat64;
Native OS Integer Types
These types are most appropriate for automatic variables. They are guaranteed to be at least 16 bits, though various architectures may define them to be wider (for example, 32 or even 64 bits). These types are never valid for fields of a structure.
Syntax
#include <prtypes.h>
typedef int PRIntn; typedef unsigned int PRUintn;
Miscellaneous Types
Size Type
PRSize
A type for representing the size of an object (not the size of a pointer). This is the
same as the corresponding type in lib.c.
Syntax
#include <prtypes.h>
typedef size_t PRSize;
Pointer Difference Types
Types for pointer difference. Variables of these types are suitable for storing a
pointer or pointer subtraction. These are the same as the corresponding types in
libc.
PRPtrdiff
Signed pointer difference type.
Syntax
#include <prtypes.h>
typedef ptrdiff_t PRPtrdiff;
PRUptrdiff
Unsigned pointer difference type.
Syntax
#include <prtypes.h>
typedef unsigned long PRUptrdiff;
Boolean Types
Type and constants for Boolean values.
PRBool
Boolean value.
Syntax
#include <prtypes.h>
typedef enum { PR_FALSE = 0, PR_TRUE = 1 } PRBool;
Description
Use PRBool for variables and parameter types. Use PR_FALSE and PR_TRUE for
clarity of target type in assignments and actual arguments. Use if (bool), while (!bool),
(bool) ? x : y, and so on to test Boolean values, just as you would C
int-valued conditions.
PRPackedBool
Packed Boolean value.
Syntax
#include <prtypes.h>
typedef PRUint8 PRPackedBool;
Description
Use PRPackedBool within structures where bit fields are not desirable but
minimum and consistent overhead matters.
Status Type for Return Values
PRStatus
Type for status code returned by some functions.
Syntax
#include <prtypes.h>
typedef enum { PR_FAILURE = -1, PR_SUCCESS = 0 } PRStatus;