How to convert gchar* to char

Question

When I press a key(integer) on my keyboard. It does something like:

 gchar *keypressed;
 keypressed=gdk_keyval_name (event->keyval);
 printf("The KeyEvent is: %s\n", keypressed); // Till here it is fine

I get segmentation fault when I do this:

char ch;
sprintf(ch, "%s\n", keypressed);   
printf("The NewKeyEvent is: %s\n",ch);

I need to convert it as I am going to use the value in a switch case. Without converting it is not possible.

Your variable `ch` is a *single character*, it can't contain a string or be used as a string. Maybe you want an *array* of characters (e.g. `char str[32];`)? — Some programmer dude, Sep 12 '15 at 09:23
Can you show me? Whatever it may be, I need the value stored on **keypressed** should be able to use in a switch case. — djgharphalia07, Sep 12 '15 at 09:28
@djgharphalia07 then use a single char . But here `keypressed` has what length ? — ameyCU, Sep 12 '15 at 09:29
@ameyCU at present **keypressed** may be a single integer number from 1-9. — djgharphalia07, Sep 12 '15 at 09:40
@user3121023 It will be same using instead of **keypressed**? isn't it? — djgharphalia07, Sep 12 '15 at 09:42
lets see then. I thought it will a char so cant be used in a switch :) — djgharphalia07, Sep 12 '15 at 09:47
Let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/89448/discussion-between-djgharphalia07-and-user3121023). — djgharphalia07, Sep 12 '15 at 09:57

score 2 · Accepted Answer · answered Sep 12 '15 at 09:25

2

gchar is a typedef alias of char, so the problem is not with the type conversion. You need to allocate some space for the sprintf buffer.

Currently, you are passing a single uninitialized char to where a pointer should be. You should get a warning from the compiler, in addition to a segfault caused by undefined behavior.

To fix this, make an array of chars and pass it to sprintf instead:

char ch[10];
sprintf(ch, "%8s\n", keypressed);   
printf("The NewKeyEvent is: %s\n", c);

Note the limit of 8 in the sprintf. This is because ch is of size 10, and we need two extra spots for '\n' and '\0'.

answered Sep 12 '15 at 09:25

Sergey Kalinichenko

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"I need to convert the it as I am going to use the value in a switch case. Without converting it is not possible." This wouldn't help you with the switch, though, because you cannot switch on a C string. You should switch on `event->keyval` itself, which has an integral type, and can be used as a `switch` expression. – Sergey Kalinichenko Sep 12 '15 at 09:49
I have converted using *atoi* and it is working fine now... event->keyval will be used soon :) – djgharphalia07 Sep 12 '15 at 12:56
When I do press 2 from the keyboard above the letters. The event->keyval *takes* it as a char value of decimel number 50. What should I do? – djgharphalia07 Sep 16 '15 at 07:06
@djgharphalia07 Isn't that what it supposed to do? Decimal number 50 corresponds to character `'2'` in [ASCII](http://www.asciitable.com/). – Sergey Kalinichenko Sep 16 '15 at 09:07
Yes! I know. I mean to say if I use *event->keyval* . Here too I have to convert the values. isn't it? So same thing. – djgharphalia07 Sep 16 '15 at 09:14
1

@djgharphalia07 That depends on what you wish to do with it. If you write `switch(event->keyval) { case '0': ... break; case '1': ... break; case '2': ... break; ... default: }` (note the single quotes around digits) you would switch on the numeric value of the digit, not on its code. – Sergey Kalinichenko Sep 16 '15 at 09:20
I faced errors when I tried this the 1st time infact :( – djgharphalia07 Sep 16 '15 at 09:48

score 1 · Answer 2 · answered Sep 12 '15 at 09:33

If you want only a single character from the keypressed string there are two ways:

Use array indexing, this way you can access any character in the string:
```
char ch = keypressed[x];  // Where `x` is the character number you want
```
_{Remember that array indexing starts from zero, so the first character in the string is number 0.}
If you want the first character, you can also use the dereference operator
```
char ch = *keypressed;
```
This equivalent to
```
char ch = keypressed[0];
```

How to convert gchar* to char

2 Answers2