A single statement without main function in c


 
Thread Tools Search this Thread
Top Forums Programming A single statement without main function in c
# 1  
Old 08-03-2015
Question A single statement without main function in c

A sample.c file is written with only one single statement.
Code:
main;

Segmentation fault occurred when executed that file.

Any statement other than
Code:
main;

is written, for example
Code:
unix;

then it won't compile.

why is this behaviour !
# 2  
Old 08-03-2015
read some book on C Smilie C program must have main() function to run. With this statement

Code:
main;

you define a symbol with name "main". Both link and compiler require this symbol and you defined it. That's why compilation and linkage works. But when you start the compiled program it tries to call the function with the name "main". It finds the symbol main in the symbol table and makes jump to the symbol definition. But because you didn't define the symbol as function it is unpredictable what is now held in the memory under the symbol main. Hopefully nulls. As result you receive core dumped, because kernel can't execute nulls or finds no instruction to execute.

When you write "unix" instead of "main", you didn't define "main" symbol and the program can't be compiled without main.

Last edited by rbatte1; 08-06-2015 at 09:59 AM..
This User Gave Thanks to agent.kgb For This Post:
# 3  
Old 08-03-2015
Code:
int main()
{
    return 0;
}

This is the most "minimal" legal C program. It is not obvious but main is in fact a function, not the real beginning of the compiled code. When you link a C program the linker adds (something like) two functions: _start() and _end() The actual names are implementation dependent. _start() sets up a lot of memory objects and files like stdout and stdin _end() cleans up after _start()

If main is not fully declared you get undefined behavior. Undefined behavior is just that - the program may dump core, panic the kernel, format your disk, or send family pictures to the Mars explorer.
This User Gave Thanks to jim mcnamara For This Post:
Login or Register to Ask a Question

Previous Thread | Next Thread

10 More Discussions You Might Find Interesting

1. UNIX for Beginners Questions & Answers

A function that refuses to run anywhere else but main()

Hi. I have some code, that for some reason, I could not post it here in this post. Here's the address for it: #if 0 shc Version 4.0.1, Generic Shell Script Compiler GNU GPL Version 3 Md - Pastebin.com First off, I used "shc" to convert the code from shell script to C. And The... (6 Replies)
Discussion started by: ignatius
6 Replies

2. UNIX for Dummies Questions & Answers

[ksh93+] Array fed by function is empty when used in main.

I feel that i am missing something obvious but i can't find what is wrong. I have a script that is launching some functions with "&" and each call is feeding the array with a value. When all calls are finished I just want to retrieve the values of that array. It is looking like that : ... (5 Replies)
Discussion started by: bibou25
5 Replies

3. AIX

Calling functions from main program from dlopened library function

Hello All, I am trying to call a function from the calling main program from a dlopened library function, below is the entire code, when I execute it it crashes with sigill. Can you guys help me out I guess I am missing out on the linker flag or something here. besides I am new to AIX and... (1 Reply)
Discussion started by: syedtoah
1 Replies

4. Programming

Function main returning int?

H friends, As we know, a function returns a value and that value is saved somwhere. like int Sum( int x, int y ) { return x + y; } Total = Sum( 10, 20 ); The value 30 is saved in variable Total. Now the question is, what int value does the function main return, and where is it... (5 Replies)
Discussion started by: gabam
5 Replies

5. Programming

How to access argv[x] from another function other than main???

Hi friends, when I am passing arguments to main, I want another function to be able to have access to that function, the problem is that I am creating athread, which has a function like void *xyz(void *), how can pass the refernce of argv to this function, if you see my program, you will better... (2 Replies)
Discussion started by: gabam
2 Replies

6. Programming

unable to send a char parameter from main to a function

why does this not work? #include <stdio.h> #include <stdlib.h> char getFileMode(char charChanger) { char filetype; /*var to hold the value to be returned*/ filetype = charSetter; /*set filetype to "l" if it is a symlink*/ return filetype; } int main(void){ char... (8 Replies)
Discussion started by: bluetxxth
8 Replies

7. Shell Programming and Scripting

Help in separating variables declared in the main function

Hi! I've a C program as shown below.. The line numbers and the statements of the program are separated by a space.. 1 #include<stdio.h> 2 char a,b,c; 3 float x,y,z; 4 int main() 5 { 6 int d,e,f; 7 // further declarations 8 // further declarations 9 /* body*/ 10 } 11 void fun1() 12... (1 Reply)
Discussion started by: abk07
1 Replies

8. Programming

signal handling while in a function other than main

Hi, I have a main loop which calls a sub loop, which finally returns to the main loop itself. The main loop runs when a flag is set. Now, I have a signal handler for SIGINT, which resets the flag and thus stops the main loop. Suppose I send SIGINT while the program is in subloop, I get an error... (1 Reply)
Discussion started by: Theju
1 Replies

9. Programming

main function

Is it possible to execute any function before main() function in C or C++. (6 Replies)
Discussion started by: arun.viswanath
6 Replies

10. Programming

c++ calling main() function

i just finished a project for a c++ class that i wrote at home on my computer, compiled with gcc. when i brought the code into school it would not compile, it would complain that cannot call main() function. at school we use ancient borland c++ from 1995. anyway my program has 20 different... (3 Replies)
Discussion started by: norsk hedensk
3 Replies
Login or Register to Ask a Question