All data shared between different compilation units comprises scalars and pointers to vectors stored in a pre-arranged place in the global vector. There are no user-declarable global variables instead, there is a global vector, similar to "blank common" in Fortran. īCPL handles bindings spanning separate compilation units in a unique way. Later, two language features were added: the bit-field selection operator and the infix byte indirection operator (denoted by %). One was by providing standard library routines for packing and unpacking words into byte strings. The mismatch between BCPL's word orientation and byte-oriented hardware was addressed in several ways. (For example, + added two values together, treating them as integers ! indirected through a value, effectively treating it as a pointer.) In order for this to work, the implementation provided no type checking. The interpretation of any value was determined by the operators used to process the values. This choice later proved to be a significant problem when BCPL was used on machines in which the smallest addressable item was not a word but a byte or on machines with larger word sizes such as 32-bit or 64-bit. For many machines of the time, this data type was a 16-bit word. The language is unusual in having only one data type: a word, a fixed number of bits, usually chosen to align with the architecture's machine word and of adequate capacity to represent any valid storage address. This approach became common practice later (e.g. Only 1⁄ 5 of the compiler's code needed to be rewritten to support a new machine, a task that usually took between 2 and 5 person-months. The back end took the O-code and translated it into the machine code for the target machine. It was split into two parts: the front end parsed the source and generated O-code, an intermediate language. A major reason for the compiler's portability lay in its structure.
BCPL was thus a popular choice for bootstrapping a system. Furthermore, the original compiler, itself written in BCPL, was easily portable. ( January 2017) ( Learn how and when to remove this template message)īCPL was designed so that small and simple compilers could be written for it reputedly some compilers could be run in 16 kilobytes. Unsourced material may be challenged and removed. Please help improve this article by adding citations to reliable sources. This section needs additional citations for verification.
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