How the main() function is called in the C/C++ language ?
How the main() function is called in the C/C++ language ?
The main() function or complete C program is treated as a normal procedure/ process. Let us understand this more clearly
#include<stdio.h> #include<stdlib.h> int main() { printf("Hello Codiens"); return 0; }
When we invoke the compiler to compile the source code, it will start compilation from the main() function and return assembly code. You can get assembly code by executing this command gcc -S filename.c or gcc -S -o filename.asm filename.c in your terminal.
You can read more about C compilation to understand it completely.
.file "main.c" .def ___main; .scl 2; .type 32; .endef .text LC0: .ascii "Hello world!\12\0" .globl _main .def _main; .scl 2; .type 32; .endef _main: pushl %ebp movl %esp, %ebp subl $8, %esp andl $-16, %esp movl $0, %eax movl %eax, -4(%ebp) movl -4(%ebp), %eax call __alloca call ___main movl $LC0, (%esp) call _printf movl $0, %eax leave ret .def _printf; .scl 2; .type 32; .endef
Then further the assembler converts the above assembly code to the machine code. At this phase, only concrete code is converted into machine language, the library functions like scanf() and printf() are not resolved yet.
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After this the above assorted code will go to the linker and it will attach the function calls with their function definition. And then gives us executable code which is pure machine code.
Now, when we get the executable code and run it. At this state, the operating system handles the request and the executable code will load in the main memory and then the address of the first instruction of the executable code gets stored in the program counter (PC is an instruction address register which holds the process first instruction address).
Then the Processor first fetches the instruction from the address stored in the program counter and the fetched instruction is then decoded so that it can be well interpreted by the microprocessor. Once it is decoded, the execution takes place and the PC (program counter) increments so that it contains the address of the next instruction of executable code.
In this section the compiler decides which will be the first instruction of the c/c++ program.
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