1. Accomplishing Executables
Briefly how this is done
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2. Introduction
An executable program is a series of bits that is perfectly understandable to a machine
Most programs need to be coded in a textual or graphical fashion to be done by people
This presentation considers how this transformation occurs
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3. Types of Transformers
There are two basic classes of program that accomplish this transformation:
Interpreters
Compilers
There are many combinations of these two
We shall look at several examples
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4. Definitions Machine language is the only language a CPU may execute
Completely different for different types of CPUs
An interpreter takes in a source language program
It executes it as if it were machine language program
A compiler translates the source language from one form to another
Most often the result is machine language
Translating from a new or rare language to a common one has been done
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5. Interpreters An interpreter takes a command and executes it directly
The early BASICs were of this form
JavaScript does this as well
The interpreter is part of the web browser
This is an excellent debugging environment
Not as fast, because the parsing of the source code takes time
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6. Simple Interpreter BASIC Interpreter BASIC Source Statements
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7. Compilation Interpretation is like the butler
You tell them to do something he does it
Compilation is like a translator
Convert a program in one language to that of another
Usually the result is machine language
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8. Several Steps Take the source language and convert into object code
Take several object codes and libraries and link together into an executable
Load the executable and run
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9. Compilation Editor Compiler Linker Loader Source Library Object
Executable
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10. Compile Cycle The compiler translates the source into object
Object is machine language
Not yet executable
Linker takes one or more objects and libraries and creates the executable
Loader executes
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11. project.cpp #include <iostream.h> … int main(void){
cout << “Enter a value”;
int a, b; cin >> a >> b; }
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12. Source and Object Inside that code were several types of routines
The main function was a function that must be externally declared
The cin and cout types are well known externals
Brought in through an include
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13. Object file
When the C++ compiler executes it compiles project.cpp and produces and object file
.OBJ on windows and .o on UNIX
This object file is mostly machine language
It also contains a relocation dictionary and an external symbol dictionary
These are structures we will not worry about
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14. Linker Takes the object files and creates an executable
Reads in the object from project.cpp places in a file
Finds from a library all of the routines that it needs for this program and places them in the file
The cin >> function and cout
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15. Loader Usually invisible to most of us Takes an executable:
Part of the OS
Takes an executable:
Relocates it, if needed
Allocates memory for it
Creates a process to start it
Starts it
Cleans up when complete
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16. Some More Thoughts
The preprocessor is one additional step in the process
Dev is an IDE
Interactive Development Environment
It manages all the pieces
Includes an editor
Executes the compiler, linker, etc.
Keeps us from having to fuss with a lot of details
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17. Finally There have been many variations on the themes given here
Any interactive program can be considered an interpreter of sorts
The need for speed has greatly reduced
One of the reasons for scripting languages popularity as well as Java
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