strcpy on a string pointer gives errors

Question

I have read a lot about the subject and I am confused .

What used to work in a C file ,not working on a cpp file :

 char  *builtinFunctions[20];

Then I get error on the strcpy function here :

void Intepreter::setBuiltIns(char *builtins)
{
   strcpy(builtinFunctions, builtins); // no matching function call to strcpy
}

I probably don't understand the basics here, but why in C++ this will not work ( do i need to use = instead ? )

strcpy(char *, const char*) = thats the structure

if I change the builtinFunctions from being a pointer it works.

EDIT: The reason for being a const before this edit is that I read here : Why is conversion from string constant to 'char*' valid in C but invalid in C++

that char *builtinFunctions[20]; will produce warning when :

builtinFunctions[0]="me";

and it did. I could fix it by removing the const .

This wouldn't work in C either. What's the type of `builtinFunctions`? — Barry, Aug 01 '16 at 12:12
So can you help me understand what am I doing wrong ? ( the const on the variable is needed in c++ compiler otherwise you get a warning) — Curnelious, Aug 01 '16 at 12:13
@Curnelious, after your edit, it's not a pointer. It's an array of pointers. — StoryTeller - Unslander Monica, Aug 01 '16 at 12:18
I read here : http://stackoverflow.com/questions/20944784/why-is-conversion-from-string-constant-to-char-valid-in-c-but-invalid-in-c that if its not a const you get an error when trying to change it. — Curnelious, Aug 01 '16 at 12:19
@Curnelious (a) An array of things is not the same as a single thing. (b) You'll get an error in that question even if it is const, since it's pointing to a literal. — StoryTeller - Unslander Monica, Aug 01 '16 at 12:21
You declare a c-style string as `char builtinFunctions[20];`. But as you are using C++, consider using `std::string`. — 001, Aug 01 '16 at 12:21
I know , I am sorry. I got confused by everything. The edit is just a note. sorry. The reason for using a pointer was because this is an array of words, not characters , so should I use instead something like builtinFunctions[20][10] ? — Curnelious, Aug 01 '16 at 12:28

Igor S.K. · Accepted Answer · 2016-08-01T12:51:45.210

This is an array of pointers to char.

char  *builtinFunctions[20];

So you call

strcpy(builtinFunctions, builtins);

gets treated as strcpy(char **, char*), not as strcpy(char *dest, const char *src). So you get a mismatch for first parameter type.

EDIT:

So let's suppose builtinFunctions is "an array of words" you wish to populate, with void Intepreter::setBuiltIns(char *builtins) meant to do just that with it's first parameter being a pointer to a new incoming word. (And you're doing this in a C-style manner. Well, up to you.)

Some things to consider.

If you declare an array type arrName[N]; then the array's name being used all alone without index is treated as a variable of type type *arrName. If you type is initially char *, then builtinFunctions by itself is of type char**. That's why your strcpy fails, but strcpy(builtinFunctions[someIndex], builtins); works.
Before invoking strcpy you should consider, if you have a destination space allocated. builtinFunctions[someIndex] is of type char *. Where does it point to? Is it a valid pointer to an allocated space, or a gateway to hell of undefined behaviour strcpy will happily take you to?

So how would you copy a new value to this pointer in this function ? should I change it from being a pointer ? it should be an array of words, this is why I used a pointer ( e.g { "aaa","bob",); — Curnelious, Aug 01 '16 at 12:23

strcpy on a string pointer gives errors

1 Answers1