Incompatible function pointer types when making array of pointers

Question

I'm working on creating a basic shell in C, running into issues when compiling with gcc:

This is the warning from my IDE:

[query] incompatible function pointer types initializing 'const void (*)(char **)' with an expression of type 'void (*)(char **)' [-Wincompatible-function-pointer-types]

This is the error I'm getting when attempting make a pull request with a json test file set up:

 grsh.c:28:48: error: initialization from incompatible pointer type [-Werror=incompatible-pointer-types]

   const void (*command_functions[]) (char **) = {&exit_shell, &change_directory, &set_path};
                                                  ^
  grsh.c:28:48: note: (near initialization for 'command_functions[0]')
  grsh.c:28:61: error: initialization from incompatible pointer type [-Werror=incompatible-pointer-types]
   const void (*command_functions[]) (char **) = {&exit_shell, &change_directory, &set_path};

Particular line of code in question:

const void (*command_functions[]) (char **) = {&exit_shell, &cd, &set_path};

I'll be 100%, not exactly sure what the issue here is. The program compiles and runs within Repl.it when running a normal compile command, but runs into issues when attempting to compile with -Werror and -Wall

Would love to get some feedback on how to properly initialize an array of pointers with type char.

Please edit your question to show more context of your code. Preferably a proper minimal reproducible example. — Some programmer dude
– Some programmer dude, Commented Nov 15, 2020 at 0:24
You do not need & to take the addresses of the functions; … = { exit_shell, change_directory, set_path }; will work just as well. A function designator is automatically converted to the address of its function except when used with sizeof or &. (Since the designator is converted to an address, *exit_shell takes the address and attempts to make it the function again, but that is automatically converted to the address. So you can write ***********exit_shell, and it will still be the address. For example, you can call the sine routine as (*************sin)(x).) — Eric Postpischil
– Eric Postpischil, Commented Nov 15, 2020 at 1:01

dxiv · Accepted Answer · 2020-11-15 00:29:48Z

2

const void (*command_functions[]) (char **) = { /*...*/ };

The posted code copied above declares command_functions as an array of pointers to functions returning const void (which is legal, albeit uncommon, see for example this answer).

To declare command_functions as an array of const pointers to functions returning void use the following, instead.

void (*const command_functions[]) (char **) = { /*...*/ };

answered Nov 15, 2020 at 0:29

dxiv

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1 Comment

Soup Over a year ago

Warning went away in IDE and compiles. Thank you for the clarification!

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