And somewhere around the time of 05/14/2004 00:23, the world stopped and
listened as Stephen Sprunk contributed the following to humanity:
The same magical fairy that calls _start() on your implementation.
Of course, since most OSes need to support binaries from arbirary languages,
picking a fixed name for program entry and using it for the C compiler's
runtime startup module is an obvious choice (though not the only one).
Runtime code for other languages would do something else if they have no
special meaning for the "main" label.
However, the short answer to the OP's question is "because the Standard says
so."
S
The main() function is used by the C/C++ compiler to designate the entry
point of the program to the linker in either a.out, object, or obj
format. From the Unix environment, the ELF header specifies the entry
point of the program. Even in DOS/Windows, there is a field in the EXE
header that's labeled entry point. Here's a segment of the man elf page
on my FreeBSD Unix system:
Elf32_Addr Unsigned program address
Elf32_Half Unsigned halfword field
Elf32_Off Unsigned file offset
Elf32_Sword Signed large integer
Elf32_Word Field or unsigned large integer
Elf32_Size Unsigned object size
typedef struct {
unsigned char e_ident[EI_NIDENT];
Elf32_Half e_type;
Elf32_Half e_machine;
Elf32_Word e_version;
Elf32_Addr e_entry; **** Entry Point
Elf32_Off e_phoff;
Elf32_Off e_shoff;
Elf32_Word e_flags;
Elf32_Half e_ehsize;
Elf32_Half e_phentsize;
Elf32_Half e_phnum;
Elf32_Half e_shentsize;
Elf32_Half e_shnum;
Elf32_Half e_shstrndx;
} Elf32_Ehdr;
e_entry - This member gives the virtual address to which the system
first transfers control, thus starting the process. If the file has no
associated entry point, this member holds zero.
For the C/C++ programming language, it is defined that main() designates
start of execution of the program, which is called by the operating
system. The program header, which is produced by the linker, and is
programming language independent, gives the operating system all the
info it needs to properly load and execute the program.
#include <stdio.h>
int main() <--- Entry Point
{
printf("Hello World\n");
return(0);
}
In Pascal (My forte, and off topic in this group), the outermost begin
statement denotes the entry point.
Program Hello(Input, Output);
Begin <--- Entry Point
Writeln("Hello World");
End.
HTH.
