Pass a pointer to a function as read-only in C

Question

Just as the title says, can I pass a pointer to a function so it\'s only a copy of the pointer\'s contents? I have to be sure the function doesn\'t edit the contents.

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Answer 1

Yes,

void function(int* const ptr){
    int i;
    //  ptr = &i  wrong expression, will generate error ptr is constant;
    i = *ptr;  // will not error as ptr is read only  
    //*ptr=10;  is correct 

}

int main(){ 
    int i=0; 
    int *ptr =&i;
    function(ptr);

}

In void function(int* const ptr) ptr is constant but what ptr is pointing is not constant hence *ptr=10 is correct expression!

---

void Foo( int       *       ptr,
          int const *       ptrToConst,
          int       * const constPtr,
          int const * const constPtrToConst )
{
    *ptr = 0; // OK: modifies the "pointee" data
    ptr  = 0; // OK: modifies the pointer

    *ptrToConst = 0; // Error! Cannot modify the "pointee" data
    ptrToConst  = 0; // OK: modifies the pointer

    *constPtr = 0; // OK: modifies the "pointee" data
    constPtr  = 0; // Error! Cannot modify the pointer

    *constPtrToConst = 0; // Error! Cannot modify the "pointee" data
    constPtrToConst  = 0; // Error! Cannot modify the pointer
} 

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