How To Write A "C" Program Without A Main Function

How To Write A "C" Program Without A Main Function

Is it possible to do

that.Yes there can be a C program

without a main function.Here’s the

code of the program without a main

function… #include #define decode(s,t,u,m,p,e,d)

m##s##u##t

#define begin decode(a,n,i,m,a,t,e) int begin()

{

printf(” hello “);

} Does the above program run without

the main function? Yes, the above

program runs perfectly fine even

without a main function.But

how,whats the logic behind it? How

can we have a C program working without main ? Here we are using preprocessor

directive #define with arguments to

give an impression that the program

runs without main.But in reality it runs

with a hidden main function. The ‘##‘ operator is called the token

pasting or token merging

operator.That is we can merge two or

more characters with it. NOTE: A Preprocessor is program which

processess the source code before

compilation. Look at the 2nd line of program- #define decode(s,t,u,m,p,e,d)

m##s##u##t What is the preprocessor doing

here.The macro decode(s,t,u,m,p,e,d) is

being expanded as “msut” (The ##

operator merges m,s,u & t into

msut).The logic is when you pass

(s,t,u,m,p,e,d) as argument it merges the 4th,1st,3rd & the 2nd characters

(tokens). Now look at the third line of the

program- #define begin decode(a,n,i,m,a,t,e) Here the preprocessor replaces the

macro “begin” with the expansion

decode(a,n,i,m,a,t,e).According to the

macro definition in the previous line

the argument must de expanded so

that the 4th,1st,3rd & the 2nd characters must be merged.In the

argument (a,n,i,m,a,t,e) 4th,1st,3rd &

the 2nd characters are ‘m’,'a’,'i’ & ‘n’. So the third line “int begin” is replaced

by “int main” by the preprocessor

before the program is passed on for the

compiler.That’s it… The bottom line is there can never exist

a C program without a main

function.Here we are just playing a

gimmick that makes us beleive the

program runs without main function,

but actually there exista a hidden main function in the program.Here we are

using the proprocessor directive to

intelligently replace the word begin”

by “main” .In simple words int

begin=int main.