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In C and C++, constructs such as pointer type conversion and union — C++ adds reference type conversion and reinterpret_cast to this list — are provided in order to permit many kinds of type punning, although some kinds are not actually supported by the standard language. In the Pascal programming language, the use of records with variants ...
The original Pascal definition appeared in 1969 and a first compiler in 1970. The first version of C appeared in 1972. Both are descendants of the ALGOL language series. ALGOL introduced programming language support for structured programming, where programs are constructed of single entry and single exit constructs such as if, while, for and case.
The XML Schema Definition language provides a set of 19 primitive data types: [17] string: a string, a sequence of Unicode code points; boolean: a Boolean; decimal: a number represented with decimal notation; float and double: floating-point numbers; duration, dateTime, time, date, gYearMonth, gYear, gMonthDay, gDay, and gMonth: Calendar dates ...
However, in some commercial and open source Pascal (or derivatives) compiler implementations —like Free Pascal, [23] Turbo Pascal or the Object Pascal in Embarcadero Delphi— a pointer is allowed to reference standard static or local variables and can be cast from one pointer type to another.
Delphi – Object Pascal is essentially its underlying language. Free Pascal compiler (FPC) – Free Pascal adopted the standard dialect of Borland Pascal programmers, Borland Turbo Pascal and, later, Delphi. PascalABC.NET – a new generation Pascal programming language including compiler and IDE.
See Unit type#In programming languages for a comparison. C and C++ also support the pointer to void type (specified as void *), but this is an unrelated notion. Variables of this type are pointers to data of an unspecified type, so in this context (but not the others) void * acts roughly like a universal or top type.
In C++, classes can be forward-declared if you only need to use the pointer-to-that-class type (since all object pointers are the same size, and this is what the compiler cares about). This is especially useful inside class definitions, e.g. if a class contains a member that is a pointer (or a reference) to another class.
Function pointers allow different code to be executed at runtime. They can also be passed to a function to enable callbacks. Function pointers are supported by third-generation programming languages (such as PL/I, COBOL, Fortran, [1] dBASE dBL [clarification needed], and C) and object-oriented programming languages (such as C++, C#, and D). [2]