CFortran

CFortran refers to the set of conventions, practices, and tools used to enable interoperability between the C and Fortran programming languages. It covers the mechanisms by which routines and data can be shared across language boundaries in a single program, allowing, for example, a C program to call Fortran subroutines or a Fortran program to invoke C functions.

Historically, inter-language calls relied on compiler-specific name mangling, calling conventions, and ad hoc wrappers, which created portability and maintenance challenges across platforms. As a result, early C-Fortran interoperability was often nonstandard and error-prone. The development of formal standards, particularly Fortran 2003’s ISO_C_BINDING, has provided a robust, portable framework for C-Fortran interaction.

In modern practice, interoperability typically involves Fortran procedures annotated with the bind(C) attribute to expose a C-compatible interface, and corresponding C declarations that match the Fortran types using definitions from the ISO_C_BINDING module (such as c_int, c_double, and c_ptr). This standard approach clarifies how data types map between the languages and how memory layout, calling conventions, and symbol visibility are handled. Important considerations include the difference in array storage order (Fortran’s column-major versus C’s row-major), argument passing semantics (Fortran default is pass-by-reference), and string handling.

CFortran interoperability is widely used in scientific and high-performance computing, where legacy Fortran numerical libraries are integrated with C or C++ code, enabling reuse and performance while maintaining a cohesive software stack. While nonstandard wrappers still exist for older compilers, ISO_C_BINDING has become the preferred method for portable cross-language calls.