Where are functions stored in memory in c? Can anyone explain it in simply language?
#include stdio.h>
void g()
{
int a=7;
}
int main()
{
printf("%d\n",sizeof(g()));
printf("%p",&g);
return 0;
}
The output of the following program is
1
00007ff6ee001581
and where the variable inside the function is stored and linked with function address
CodePudding user response：
The variable inside function are stored in stack.
And every linking and addressing part is done by linker.
In simple words linker decides what absolute address to give to what label or function and compiler decides how they will be arranged and will be able to address each other.
Compiling takes four steps:
Preprocessing [in which header file and microprocessor worked upon].
Compiling[In which they are converted into assembly code]
Assembly[In which codes are converted into machine level language but have relative addressing in respect to there starting]
Linking[When absolute address is given so when loaded they can address each other and files and linked in one]
#I think these last lines can help you
Functions and variable are labels and every label is translated into address. The code that runs on machine have address that represent these labels. And not only c but every compiled language goes through it. As on machine its machine code or just wiring.
Say if you not understood anything. Will be glad to help you
CodePudding user response：
The output of the following program is
The second line of output is a pointer to the code for the function g. It's the address of that function, and it's the literal the answer to your question about where the function is stored.
and where the variable inside the function is stored and linked with function address
The variable a is a local variable, so it only exists while the function is executing. Usually the compiler will create space for local variables on the stack -- that's one of the main reasons for having a stack. Once the function returns, its local variables are popped off the stack and they cease to exist. In other words, a isn't connected to the location of g at all.
Local variables are typically referenced via some offset from the stack pointer. When you call a function, a stack frame is created on the stack. The stack frame basically consists of storage for all the function's local variables, and also the address of the previous stack pointer and the return address. The function's code then starts executing, and since the compiler knows the relative address of each variable (i.e. where it is in the stack frame), it can easily calculate the absolute address. Most processors have instructions that make relative addressing easy for exactly this reason. When the function exits, the stack pointer is set back to the previous stack frame and the processor jumps to the return address. But this is just one possible implementation; on modern processors that have lots of registers, local variables may not even be stored on the stack -- they may just end up in registers.
CodePudding user response：
include <stdio.h>
void g()
{
int a=7;
}
int main()
{
//printf("%d\n",sizeof(g()));
//you cant use sizeof(g()) its a functiona and
//function not have anysize
printf("%p",&g);
//even you can't use here int a=7 that you declared in void g() as it is local to
//that function and this function cant access any function local variable
//but what it returns
return 0;
}
If you want to see addressing than see this:
0000000000001135 <g>:
1135: 55 push %rbp
1136: 48 89 e5 mov %rsp,%rbp
1139: c7 45 fc 07 00 00 00 movl $0x7,-0x4(%rbp)
1140: 90 nop
1141: 5d pop %rbp
1142: c3 retq
0000000000001143 <main>:
1143: 55 push %rbp
1144: 48 89 e5 mov %rsp,%rbp
1147: 48 8d 35 e7 ff ff ff lea -0x19(%rip),%rsi # 1135 <g>
114e: 48 8d 3d af 0e 00 00 lea 0xeaf(%rip),%rdi # 2004
<_IO_stdin_used 0x4>
1155: b8 00 00 00 00 mov $0x0,