Re: [Dev-C++] A basic q...

[Luigi S. <gi...@li...>]

Hello Daniel,

A makefile is a set of instructions (a program if you wish) that will be 
interpreted by a program generally known as "make".

"make" is a general tool, not strictly related to programming languages, 
but undoubtedly one is likely to run into it when dealing with "compiled" 
programming languages.

Here is what I mean.

Consider the classic "BASIC" programming language (hope you know a little 
about it), a program written with such language is a set of instructions 
which a BASIC interpreter reads and executes, one at a time, each time you 
run the program. There is no executable file and to run a program you 
always need: the source code and the interpreter. Also, if a program has 
syntax errors, you will find out about them, only when the interpreter 
executes the offending line of code; in fact only at that time it will 
realize that the instruction is wrong.

Consider instead a C (or C++) program (I mean here what is known as a 
statically linked program, that is, one which does not use any DLL). You 
write the source code, a compiler will then translate it into an object 
file which a linker will use to make an executable file. Thus the program 
is translated into machine code only once (and not each time you execute 
the program), also to execute the program, you only need the executable 
file (often called the binary file) and nothing else (this of course is not 
true of dynamically linked programs, which also require the right DLLs). 
Since to run a program, you must have compiled already *all* the 
instructions, if there are syntax errors, you will find out about them, at 
compile time, no instruction will be executed if there are syntax errors.

Now here is the reason why one uses "make" with compiled programming languages:
say that one writes some source code and then compiles it, making the 
corresponding executable file, now suppose that he makes some changes to 
the source code, what happens is that the executable file no longer 
corresponds to the source. This never happens with interpreted languages, 
because, as I said, there is no executable file for those languages.

The classic way (don't know how many still use it) to keep a binary up to 
date is to use "make". Roughly, What "make" does is the following:
- read the time stamp of the binary file
- read the time of the corresponding source file
- if the source happens to be "younger" that the binary, this latter is 
out-of-date

When the binary is out of date, the actions needed to update it will be 
performed, by "make".

Things are a bit more complicated when a program is made of code spread 
across different source files, but the basic idea is the same.

At this point you could ask:
- How does "make" know which source file is the one used to compile some 
binary file?
- How does it know which are the actions to update a binary file?

Well, you put these informations in a text file, named "makefile", 
arranging them in some special way (just the syntax understood by "make").

The above is, I hope, the frame of the picture: if you wish to fill it with 
details, you could start by reading the manual of the GNU "make" (I've 
found it on the Dev-C++ resource site).

At 14:13 09/04/02 +0100, Daniel Glenfield wrote:
>I have gaps in my knowledge lol.
>What's a MAKE file, and what does it do?




--
Luigi
gi...@li...