Quote:
| Originally Posted by jinish Explain C program execution,what are happened during executing a C program? |
Homework? You have no idea if this is jinish's homework, give him a break asterik_man, it's s simple question, that is what this whole forum is for anyway, questions.
Memory is organized into four segments:
Runtime Stack - This is used everytime a function is called, main() included. Each record on the stack is called an activation record which stores the function's parameters, the return address of the caller function, and locally defined variables, in that order.
Heap - A dynamically growing portion of memory, when you use malloc() or define an array, this is where they are stored. Advanced C programs make use of the heap, it's a pain to maintain though.
Static area - Static and global variables are stored here throughout the life of the program.
Text area - The assembly code of the program is stored here, this is for the operating system, the programmer can't access this portion of memory.
Below is an example:
C Code:
#include <stdio.h>
int foo ( int arg ) ;
int foo ( int arg ) {
int ans = 10 ;
arg += ans ;
return ans ;
}
int main ( int argc, char* argv[] ) {
int num = 5;
foo ( num ) ;
return 0 ;
}
UNIX calls main() and pushes it as an activation record on to the runtime stack. In main's activation record lies argc and argv, followed by a return address back to UNIX and the variable num. Then main() calls foo() which is also pushed on to the runtime stack as an activation record. When foo() returns it value back to main(), foo() is popped off the runtime stack and the record (activation record) of arguments passed and locally defined variables are lost forever, this is a call by value language at work. If you wish to avoid this, use pointers. Finally, when main() returns to UNIX--the return 0 is the error code--it too is popped off the runtime stack and your program is no longer running.
This is a bad explanation if you can't visualize what I'm saying. My professor had us commit to memory what it all looks like, and I haven't forgot it.
Linear Mode
