Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.c > #164629

Re: What's wrong with "char op[8]=(istest?"ef":"df");"

Show all headers | View raw

John Forkosh <forkosh@panix.com> writes:
> Minimal working (or should I say non-working example)...
>
> #include <stdio.h>
> int main () {
>   int istest=1;
>   char op[8] = (istest?"ef":"df");
>   /*char op[8] = "ef";*/
>   printf("op=%s\n",op); }
>
> for which cc emits the error...
>
> test.c: In function 'main':
> test.c:4:16: error: invalid initializer
>     4 |   char op[8] = (istest?"ef":"df");
>       |                ^
>
> But if I comment out that line and uncomment the one below it,
> then it compiles and runs fine. I've used this construction
> a million times without problems. But a-million-and-one seems
> to somehow be a problem. What's wrong???

The "=" symbol can be used either in an assignment or in an declaration
with an initializer.  They look similar, but they're different.

For example:

    int n = 42; // an declaration with an initializer
    n = 42;     // an assignment

The "=" in the declaration must be followed by an *initializer*, which
can be either an expression or a sequence of one or more initializers
enclosed in { ... }.  The "=" in the assignment must be followed by an
expression.

A declaration like

    char op[8] = "ef";

is a special case.  Arrays can be initialized, but they can't be
assigned, so this:

    op = "ef";

is invalid.  The special case is that you can use a string literal
as the initializer for an array object (of an appropriate type).
There is no such special case for more complicated expressions like
(istest?"ef":"df").

Somewhat similarly, but following from a different set of rules, this is
valid:

    int a[] = { 10, 20, 30 };

but this is not:

    int a[] = cond ? { 10, 20, 30 } : { 40, 50, 60 };

because { 10, 20, 30 } is an initializer but not an expression.

-- 
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
Working, but not speaking, for Philips
void Void(void) { Void(); } /* The recursive call of the void */

Back to comp.lang.c | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

What's wrong with "char op[8]=(istest?"ef":"df");" John Forkosh <forkosh@panix.com> - 2022-01-25 13:00 +0000
  Re: What's wrong with "char op[8]=(istest?"ef":"df");" John Forkosh <forkosh@panix.com> - 2022-01-25 13:09 +0000
    Re: What's wrong with "char op[8]=(istest?"ef":"df");" Bart <bc@freeuk.com> - 2022-01-25 14:03 +0000
      Re: What's wrong with "char op[8]=(istest?"ef":"df");" John Forkosh <forkosh@panix.com> - 2022-01-25 14:33 +0000
  Re: What's wrong with "char op[8]=(istest?"ef":"df");" Mateusz Viste <mateusz@xyz.invalid> - 2022-01-25 14:36 +0100
    Re: What's wrong with "char op[8]=(istest?"ef":"df");" John Forkosh <forkosh@panix.com> - 2022-01-25 14:41 +0000
  Re: What's wrong with "char op[8]=(istest?"ef":"df");" Tim Rentsch <tr.17687@z991.linuxsc.com> - 2022-01-25 06:39 -0800
    Re: What's wrong with "char op[8]=(istest?"ef":"df");" John Forkosh <forkosh@panix.com> - 2022-01-25 14:56 +0000
  Re: What's wrong with "char op[8]=(istest?"ef":"df");" James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-01-25 11:08 -0500
    Re: What's wrong with "char op[8]=(istest?"ef":"df");" John Forkosh <forkosh@panix.com> - 2022-01-26 08:18 +0000
  Re: What's wrong with "char op[8]=(istest?"ef":"df");" Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-01-25 14:37 -0800
    Re: What's wrong with "char op[8]=(istest?"ef":"df");" John Forkosh <forkosh@panix.com> - 2022-01-26 08:27 +0000
  Re: What's wrong with "char op[8]=(istest?"ef":"df");" Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-01-25 19:49 -0800
    Re: What's wrong with "char op[8]=(istest?"ef":"df");" Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2022-01-25 19:56 -0800
    Re: What's wrong with "char op[8]=(istest?"ef":"df");" James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-01-25 23:37 -0500
      Re: What's wrong with "char op[8]=(istest?"ef":"df");" Andrey Tarasevich <andreytarasevich@hotmail.com> - 2022-01-25 20:54 -0800
    Re: What's wrong with "char op[8]=(istest?"ef":"df");" John Forkosh <forkosh@panix.com> - 2022-01-26 08:37 +0000
  Re: What's wrong with "char op[8]=(istest?"ef":"df");" Kaz Kylheku <480-992-1380@kylheku.com> - 2022-01-26 05:08 +0000
    Re: What's wrong with "char op[8]=(istest?"ef":"df");" John Forkosh <forkosh@panix.com> - 2022-01-26 09:22 +0000
  Re: What's wrong with "char op[8]=(istest?"ef":"df");" John Forkosh <forkosh@panix.com> - 2022-01-26 09:24 +0000

csiph-web