• State Not Answered
  • Locked Locked
  • Replies 7 replies
  • Subscribers 21 subscribers
  • Views 3710 views
  • Users 0 members are here
2025 survey

We are running a survey to help us improve the experience for all of our members. If you see the survey appear, please take the time to tell us about your experience if you can.

Options
Related
How was your experience today?
This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

Can I take the address of a function argument?

my tea confused

I know this isn't a Keil specific question, but I know you guys are smart and that I'll just get a direct non-mocking answer.

Is it legal to take the address of a function argument?


void Bar(unsigned char *Pointer)
{
  // Access data byte via the pointer
}

int Foo(unsigned char Arg)
{
  Bar(&Foo); // <<<<<< Is this legal?
}

I know you cannot take the address of a variable of type register and I think that knowledge is clouding my memory.

Parents
  • 0 in reply to ImPer Westermark

    OMG. I feel even more like a noobie now.

    I intended to write:

    void Bar(unsigned char *Pointer)
{
  // Access data byte via the pointer
}

int Foo(unsigned char Arg)
{
  Bar(&Arg); // <<<<<< Is this legal?
}

    Fortunately you saw my stupidity and answered it with:

    The second function takes an int - that is a local copy so you may take the address of this local variable Arg but can't return back a change.

    Thanks.

    This is what a couple of years away from serious programming has done to me :(

Reply
  • 0 in reply to ImPer Westermark

    OMG. I feel even more like a noobie now.

    I intended to write:

    void Bar(unsigned char *Pointer)
{
  // Access data byte via the pointer
}

int Foo(unsigned char Arg)
{
  Bar(&Arg); // <<<<<< Is this legal?
}

    Fortunately you saw my stupidity and answered it with:

    The second function takes an int - that is a local copy so you may take the address of this local variable Arg but can't return back a change.

    Thanks.

    This is what a couple of years away from serious programming has done to me :(

Children
  • 0 in reply to my tea confused

    Understand me correctly.

    The function Bar() can modify the parameter Arg that the function Foo() did send.

    But such a change fill not migrate back to whatever code that did call Foo(). Arg is a local variable inside Foo() and any changes to Foo() (inside Foo() or by the call to Bar()) will just happen to this local Arg. As soon as Foo() ends, the local parameter Arg will be thrown away.

    So yes - you can send the address of parameters to other functions and have these functions change the value of your parameter. The function that takes the pointer doesn't care about if the pointer points to an argument, a local variable or a global variable or even a member of a struct.

  • 0 in reply to ImPer Westermark

    So yes - you can send the address of parameters to other functions and have these functions change the value of your parameter.

    The emboldened part is the key part for me.

    Lifetime of variables is not something I'd forgotten about :)

    Thanks for taking the time to answer. I always did like your clear complete responses.

  • 0 in reply to my tea confused

    Just read few articles on "pass by value" & "pass by reference" to learn techniques of parameter passing.

    explanation with an example
    www.cprogrammingexpert.com/.../pass_by_value.aspx

    an detailed article
    courses.washington.edu/.../passby.html

    function pointer is a concept that must be learnt after learning some basics, regularly used C skills.