ObjexxFCL: Objexx Fortran Compatibility Library

The Objexx Fortran Compatibility Library (ObjexxFCL) is a C++ library providing Fortran-compatible array, string, i/o, and intrinsic function support for Fortran-to-C++ migrations. The ObjexxFCL is included with Objexx Fortran to C++ conversion projects and is used to support a range of Fortran--C++ integration goals. The ObjexxFCL components have capabilities beyond those of their Fortran equivalents that are used to support reengineering and modernization of technical C++ applications after the initial migration or integration has been completed.

The Users and Developers Guides describe the ObjexxFCL in detail. Doxygen documentation can also be generated from the source for a full navigable API.

ObjexxFCL Application Archictecture

C++ applications using the ObjexxFCL generally use the library much as the Standard C++, providing types and functions used by certain application components and subsystems. The ObjexxFCL acts much as an adapting layer between the native C++ and the portions of the application that use its services, as shown in the sidebar.

ObjexxFCL Components

The core components of the ObjexxFCL provide the array, string, and intrinsic function support for Objexx Fortran-to-C++ conversions and Fortran—C++ integration. The ObjexxFCL also contains components that support the evolution of technical applications after conversion from Fortran to C++ or as part of a modernization process. There are also components and functions that provide useful services for technical computing that C++ and its standard library are missing.

Some of the main ObjexxFCL components are described below.

FArray

FArrays have the attributes of Fortran 77 arrays, including:

• Each dimension can have an arbitrary index range.
• Column major element ordering: Nested loops ordered to provide efficient contiguous element access are still efficient in the C++.
• Array passing "tricks": Arrays and array elements can be passed to functions where they are declared with a different rank or dimensions.
• Assumed size array arguments.

Technical applications often depend on fast, safe arrays and the ObjexxFCL provides some powerful array support, such as the ability to migrate to dynamic array sizing via explicit calls or a de-centralized automatic mechanism for the common situation where the sizes for different parts of the array dimensions are determined in locations scattered throughout the code.

The FArray arrays provide these capabilities that Fortran 77 arrays lack (some of which are provided by Fortran 95/2003):

• Copy construction
• Constant arrays and array proxies
• Initializer values/functions (more powerful than DATA statements)
• Optional element initialization
• Whole-array value and array assignment
• Index range and size accessors
• Linear index subscripting for fast inner loop operations
• Array sections
• Dynamic (run-time) (re)sizing
• Automatic dynamic allocation and sizing via Dimension objects
• Optional run-time size reporting
• Bounds checking in debug builds

Fstring

Fstrings have the attributes of Fortran 77 strings, including:

• Fixed length.
• Characters are indexed starting from 1.
• "Live" substrings.
• Concatenation support.
• Trailing space ignored by comparison operations.

Formatted I/O

The ObjexxFCL provides a Fortran-like formatted read and write system that works within C++ stream-based i/o. This is designed to work in-line within stream-based i/o rather than with the separate format descriptor of Fortran 77 and C to avoid the unsafe C-style i/o and to provide a starting point for subsequent i/o evolution within the preferred C++ i/o model.

Byte

The byte type is a C++ equivalent of Fortran's INTEGER*1. The ubyte type is the unsigned variant of byte. Beyond emulating Fortran's INTEGER*1 the byte types support C++ bit operations and avoid unwanted conversions to/from the char type.

Intrinsic Functions

The ObjexxFCL provides Fortran 77 intrinsic functions.

Numeric, String, and Character Functions

In addition to the Fortran 77 intrinsic support there are numeric, string, and character functions that extend and fill holes in the C++ standard library.

ChunkVector: Very Large Vectors

ChunkVector is similar in interface to std::vector but uses multiple contiguous "chunks" of user-specified size to avoid allocation failures for very large vectors in a fragmented memory environment and to greatly reduce the performance cost of resizing operations. In typical use there is no performance degradation for ChunkVector element access compared to std::vector.

CArray & Cstring: Safe C-Style Array and String Wrappers

These are lightweight wrappers around C-style arrays and strings that catch memory errors such as leaks and buffer overflows. This allows the safe use of functions requiring those C-style types.

  ObjexxFCL Application Architecture