COUSINS OF COMPILER
1. Preprocessor 2. Assembler 3. Loader and Link-editor
A preprocessor is a program that processes its input data to produce output that is used as input to another program. The output is said to be a preprocessed form of the input data, which is often used by some subsequent programs like compilers.
They may perform the following functions :
1. Macro processing 3. Rational Preprocessors
2. File Inclusion 4. Language extension
1. Macro processing:
A macro is a rule or pattern that specifies how a certain input sequence should be mapped to an output sequence according to a defined procedure. The mapping process that instantiates a macro into a specific output sequence is known as macro expansion.
2. File Inclusion:
Preprocessor includes header files into the program text. When the preprocessor finds an #include directive it replaces it by the entire content of the specified file.
3. Rational Preprocessors:
These processors change older languages with more modern flow-of-control and data-structuring facilities.
4. Language extension :
These processors attempt to add capabilities to the language by what amounts to built-in macros. For example, the language Equel is a database query language embedded in C.
Assembler creates object code by translating assembly instruction mnemonics into machine code. There are two types of assemblers:
· One-pass assemblers go through the source code once and assume that all symbols will be defined before any instruction that references them.
· Two-pass assemblers create a table with all symbols and their values in the first pass, and then use the table in a second pass to generate code
Fig. 1.7 Translation of a statement
Linker and Loader
A linker or link editor is a program that takes one or more objects generated by a compiler and combines them into a single executable program. Three tasks of the linker are
1.Searches the program to find library routines used by program, e.g. printf(), math routines.
A loader is the part of an operating system that is responsible for loading programs in memory, one of the essential stages in the process of starting a program.
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