Incompatible pointer types on array initialization

Question

The following array initializer:

const char** AST_NODE_TYPE_NAMES = {
    "AST_NODE_CONSTANT",
    "AST_NODE_BINARY",
    "AST_NODE_UNARY",
    "AST_NODE_VARIABLE",
    "AST_NODE_ASSIGNMENT",
    "AST_NODE_STATEMENTS",
};

Makes gcc raise the following warning:

initialization of 'const char **' from incompatible pointer type 'char *'

Help me figure this out?

... but you've written an initializer for AST_NODE_TYPE_NAMES as if it were an array. — John Bollinger
– John Bollinger, Commented May 11, 2019 at 13:38

0___________ · Accepted Answer · 2019-05-11 13:50:50Z

4

you want array of pointers

const char *AST_NODE_TYPE_NAMES[] = {
    "AST_NODE_CONSTANT",
    "AST_NODE_BINARY",
    "AST_NODE_UNARY",
    "AST_NODE_VARIABLE",
    "AST_NODE_ASSIGNMENT",
    "AST_NODE_STATEMENTS",
};

and this array can eventually decal to the pointer you want:

const char **foo1 = AST_NODE_TYPE_NAMES;
const char **foo = &AST_NODE_TYPE_NAMES[0];

you can also use the compound literal (which actually is the array of pointers in this case) to initialize this pointer

const char** AST_NODE_TYPE_NAMES =(const char *[]) {
    "AST_NODE_CONSTANT",
    "AST_NODE_BINARY",
    "AST_NODE_UNARY",
    "AST_NODE_VARIABLE",
    "AST_NODE_ASSIGNMENT",
    "AST_NODE_STATEMENTS",
};

edited May 11, 2019 at 13:50

answered May 11, 2019 at 13:40

0___________

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Comments

Antti Haapala · Accepted Answer · 2019-05-11 15:25:52Z

0

A pointer is not an aggregate but a scalar, and it expects one value to initialize it. In C it is also permissible to wrap the scalar initializer in { }!

Thus:

const char** AST_NODE_TYPE_NAMES = {
     "AST_NODE_CONSTANT",
     "AST_NODE_BINARY",
     "AST_NODE_UNARY",
     "AST_NODE_VARIABLE",
     "AST_NODE_ASSIGNMENT",
     "AST_NODE_STATEMENTS",
};

tries to initialize one pointer to pointer to const char with the address of the first character of string literal "AST_NODE_CONSTANT", but that does not have type const char ** but just char *. In addition to that, there are 5 excess initializers, namely the following strings.

What you of course want to do is to initialize an array, as P__J__ already showed.

answered May 11, 2019 at 15:25

Antti Haapala

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