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IIRC, the wording of the C++ standard are vague enough to permit the this argument to be passed in a special way, but all the ABIs I heard of are passing it exactly as the first (pointer) argument of usual C functions.

IIRC, the wording of the C++ standard are vague enough to permit the this argument to be passed in a special way, but all the ABIs I heard of are passing it exactly as the first (pointer) argument of usual C functions.

The point is that this is an implicit formal parameter (containing the address of the object whose method you are calling). It is not a local variable.

You see that some space for your vec is allocated on the stack (e.g. with subq $48, %rsp etc...) and then the address of that zone on the stack is passed as the this formal argument (using the usual x86-64 ABI conventions, which dictates (p 20) that the first argument of function is passed thru register %rdi) so you could say that this is, at the beginning of some member function, in the register %rdi ...

The point is that this is an implicit formal parameter (containing the address of the object whose method you are calling). It is not a local variable.

You see that some space for your vec is allocated on the stack (e.g. with subq $48, %rsp etc...) and then the address of that zone on the stack is passed as the this formal argument (using the usual x86-64 ABI conventions, which dictates (p 20) that the first argument of function is passed thru register %rdi) so you could say that this is, at the beginning of some member function, in the register %rdi ...

IIRC, the wording of the C++ standard are vague enough to permit the this argument to be passed in a special way, but all the ABIs I heard of are passing it exactly as the first (pointer) argument of usual C functions.

BTW, you should trust the compiler and let it pass this as convenient and as prescribed by ABI specifications.

Look at the generated code of your program. I compiled (on Linux/Debian/Sid/x86-64 with [GCC][1] 4.9.1) your example arman.cc with

You see that some space for your vec is allocated on the stack (e.g. with subq $48, %rsp etc...) and then the address of that zone on the stack is passed as this [1]: http://gcc.gnu.org/

Look at the generated code of your program. I compiled (on Linux/Debian/Sid/x86-64 with GCC 4.9.1) your example arman.cc with

You see that some space for your vec is allocated on the stack (e.g. with subq $48, %rsp etc...) and then the address of that zone on the stack is passed as the this formal argument (using the usual x86-64 ABI conventions, which dictates (p 20) that the first argument of function is passed thru register %rdi) so you could say that this is, at the beginning of some member function, in the register %rdi ...