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:
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)
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)
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)
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)
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)
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)
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)
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)
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
LEARN ABOUT SUNOS
printstack
walkcontext(3C) Standard C Library Functions walkcontext(3C)NAME
walkcontext, printstack - walk stack pointed to by ucontext
SYNOPSIS
#include <ucontext.h>
int walkcontext(const ucontext_t *uptr, int (*operate_func)(uintptr_t, int, void *), void *usrarg);
int printstack(int fd);
DESCRIPTION
The walkcontext() function walks the call stack pointed to by uptr, which can be obtained by a call to getcontext(2) or from a signal han-
dler installed with the SA_SIGINFO flag. The walkcontext() function calls the user-supplied function operate_func for each routine found
on the call stack and each signal handler invoked. The user function is passed three arguments: the PC at which the call or signal occured,
the signal number that occured at this PC (0 if no signal occured), and the third argument passed to walkcontext(). If the user function
returns a non-zero value, walkcontext() returns without completing the callstack walk.
The printstack() function uses walkcontext() to print a symbolic stack trace to the specified file descriptor. This is useful for reporting
errors from signal handlers. The printstack() function uses dladdr1() (see dladdr(3C)) to obtain symbolic symbol names. As a result, only
global symbols are reported as symbol names by printstack().
RETURN VALUES
Upon successful completion, walkcontext() and printstack() return 0. If walkcontext() cannot read the stack or the stack trace appears
corrupted, both functions return -1.
ERRORS
No error values are defined.
USAGE
The walkcontext() function is typically used to obtain information about the call stack for error reporting, performance analysis, or diag-
nostic purposes. Many library functions are not Async-Signal-Safe and should not be used from a signal handler. If walkcontext() is to be
called from a signal handler, careful programming is required. In particular, stdio(3C) and malloc(3C) cannot be used.
The printstack() function is Async-Signal-Safe and can be called from a signal handler. The output format from printstack() is unstable, as
it varies with the scope of the routines.
Tail-call optimizations on SPARC eliminate stack frames that would otherwise be present. For example, if the code is of the form
#include <stdio.h>
main()
{
bar();
exit(0);
}
bar()
{
int a;
a = foo(fileno(stdout));
return (a);
}
foo(int file)
{
printstack(file);
}
compiling without optimization will yield a stack trace of the form
/tmp/q:foo+0x8
/tmp/q:bar+0x14
/tmp/q:main+0x4
/tmp/q:_start+0xb8
whereas with higher levels of optimization the output is
/tmp/q:main+0x10
/tmp/q:_start+0xb8
since both the call to foo() in main and the call to bar() in foo() are handled as tail calls that perform a return or restore in the delay
slot. For further information, see The SPARC Architecture Manual.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|Interface Stability |Stable |
+-----------------------------+-----------------------------+
|MT-Level |Async-Signal-Safe |
+-----------------------------+-----------------------------+
SEE ALSO intro(2), getcontext(2), sigaction(2), dladdr(3C), siginfo.h(3HEAD), attributes(5)
Weaver, David L. and Tom Germond, eds. The SPARC Architecture Manual, Version 9. Santa Clara: Prentice Hall, 2000.
SunOS 5.10 1 Mar 2004 walkcontext(3C)