Help writing getstring function

Question

Im having some trouble writing a getstring function, this is what I have so far.

Regards, V

const char* getstring()
{


    char *buffer;
    int i = 255;

    buffer = (char *)malloc(i*sizeof(char));

    *buffer = getchar();
    while ( *buffer != '\n' )
    {
        buffer++;
        *buffer = getchar();
    }
    *buffer = '\0';

    const char* _temp = buffer;
    return _temp;
}


int main()
{
    char* temp = getstring();

    for ( ;temp++ ; *temp != '\0')
    {
        printf("%c", *temp);
    }

    return 0;
}

score 2 · Answer 1 · edited Sep 18 '13 at 23:46

2

Why not just use

char buffer[255];
scanf("%254s", &buffer);

or

char* buffer = readline("GO GO GO:");

edited Sep 18 '13 at 23:46

Kara

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answered Apr 14 '10 at 22:15

Michael Mrozek

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Or: fgets(buffer, sizeof(buffer), stdin); – Jonathan Leffler Apr 14 '10 at 22:18
No this isn't homework. I suppose I could of mentioned that the function is to get strings from serial on an ARM MCU but I didn't think it was relevant. I dont think any of them options will work, Thanks – volting Apr 14 '10 at 22:24

caf · Accepted Answer · 2010-04-14T22:21:41.470

You're setting _temp to buffer when the latter points at the terminating '\0' of the string.

Move the line:

const char* _temp = buffer;

to be immediately after the line:

buffer = (char *)malloc(i*sizeof(char));

so that _temp is pointing to the start of the buffer.

You have some other problems:

Don't use the name _temp - names with a leading underscore are reserved;
You need to test that you don't write more than i bytes into the buffer;
You should test for malloc() returning NULL;
You need to test for getchar() returning EOF. This will mean you need to store the getchar() result in a variable of type int before you assign it to *buffer;
As Michael Mrozek points out in a comment, the expressions in your for loop are the wrong way around.

...and as a point of style, sizeof(char) is always 1, so multiplying by it is unnecessary; and casting the result of malloc() is unnecessary in C and considered undesirable (unlike C++, where it is required).

Minor sidenote not worthy of its own answer: the for loop arguments are backwards — Michael Mrozek, Apr 14 '10 at 22:17
Yes made all of the changes and its working fine now. Not sure even how the for loop got so contorted, It must of got worped at some point when I was experimenting. Thanks, V — volting, Apr 14 '10 at 22:33

N 1.1 · Answer 3 · 2010-04-14T22:23:21.097

1

const char* _temp = buffer;

Move the above statement just after the call to malloc

Important:
Free the memory allocated to buffer after its use in main().

free(temp);

edited Apr 14 '10 at 22:23

answered Apr 14 '10 at 22:17

N 1.1

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Yes forgot to do that, Thanks, V – volting Apr 14 '10 at 22:34

Jonathan Leffler · Answer 4 · 2010-04-14T22:20:42.320

0

You need to keep track of the allocated pointer - the value returned by malloc() - immediately after calling malloc() so you can pass it back to the caller. You should also check for EOF as well as newline - and that requires an int (not a char) to hold the value from getchar(). At minimum!

edited Apr 14 '10 at 22:20

answered Apr 14 '10 at 22:15

Jonathan Leffler

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Help writing getstring function

4 Answers4