Thread: Getline help

I was wondering if someone could tell me what is wrong with this code and what I could do to fix it. It says Segmentation Fault when I run it.

char * getline(char * string,int max_chars)
{
char response;
char *pstring;
*pstring = string;

if (max_chars)
{
int number;
while((response = getchar()) != '\n')
{
if (number < max_chars)
{
*pstring++ = response;
number++;
}
else
{
break;
}
}
}
else
{
while ((responce = getchar()) != 'n')
{
*pstring++ = response;
}
}
*pstring = '\0';
return string;
}

int main(void)
{
char ff[10];
getline(ff,30);
puts(ff);
return 0;
}

Code:

char * getline(char * string,int max_chars) 
{ 
    char response; 
    char *pstring; 
    *pstring = string;

Should be:

pstring = string;

Code:

   char ff[10]; 
   getline(ff,30);

Ack! What are you doing? Can you say "Buffer Overflow"? I thought you could!

Quzah.

Originally posted by Salem
> getline(ff,30);
Not lying about the size of your buffer would be a start
Try
getline(ff,10);

or
getline(ff,sizeof(ff));

http://www.cprogramming.com/cboard/m...bbcode#buttons

Fah. You beat me to it. ('m on a phone call) I tend to post and edit and post... as I read down the post at times...

Quzah.

>if (number < max_chars)
number is uninitialized here.

>while ((responce = getchar()) != 'n')
Spelling. It's response and '\n'.

-Prelude

Or you could just save yourself the trouble...

char * getline(char * string,int max_chars) { fgets( string, max_chars, stdin ); return string; }

Here's a thought: Why are you bothering to return anything?

Quzah.

The code as of now is:

#include <stdio.h>

char * getstring(char * string,int max_chars)
{
char responce;
char * pstring;
pstring = string;
int number;

while ((responce = getchar()) != '\n')
{
if (number < max_chars)
{
*pstring++ = responce;
number++;
continue;
}
else
{
break;
}
}
*pstring = '\0';
return string;
}

int main(void)
{
char ff[10];
getstring(ff,10);
puts(ff);
return 0;
}


..this doesn't work, although it DOES work if i make it:

char ff[30];
getstring(ff,30);

I want this to be able to ask for input then, once it gets a \n or after it get's to max_chars it stops allowing input and then puts() it. Any idea what the trouble is now?

char * pstring;
pstring = string;
int number;

Well, for one, that is not valid C code. It is valid in C++, but not in C (unless it's in the new standard). In C, you must declare all varaibles at the beginning of the scope, then you can make assignments.

I want this to be able to ask for input then, once it gets a \n or after it get's to max_chars it stops allowing input and then puts() it. Any idea what the trouble is now?

That depends on what you mean "ask for input then, once it gets... ...it stops allowing input". Do you mean stops reading from the keyboard? Or do you mean it's going to just ignore everything from that point on?

There is no ANSI standard for just having the program stop reading input from the keyboard. Ie: as soon as I press the key, it ignores them all if I'm past X number of characters.

Quzah.

Say I do getstring(ff,10). I want getstring to read all input until 'number' gets to 10 or if the enter key is pressed before that.

Example of what I would like it to do:

I run the function:
getstring(ff,10);

I Input:
abcdefghijklmnop <then press the enter key>

The program outputs the first 10 characters:
abcdefghij

So is there a reason you need to write your own functin? Why not just use fgets?

fgets( ff, 10, stdin );

Otherwise:

Code:

while( number < max_number-1 )
{
    string[number] = getch( );
    if( string[number] == '\n )
        break;
}
string[number] = '\0';

Remember: You must add a null. As such, you can only actually read nine characters if you pass it 10.

Quzah.

Have you now added a line like
>number = 0;
in the getstring function? In your previous posts, number was not set before it was used.

Also, the way your code works (last posting of), you exceed the buffer length if the string is longer than max_chars. This is not done with user input, but by the line
>*pstring = '\0';
This is because you took a character from the user and put it into the last char of the buffer, then incremented pstring. The next iteration of the read loop caused the break because you had read enough input, but you then went and plonked a \0 into *pstring, which is of course now pointing to one byte past the end of the array. <phew>

Post your lasted version of code if you still have problems.

I thought that if you assigned an int within a function it is automatically set to 0.

Originally posted by pr0ficient
I thought that if you assigned an int within a function it is automatically set to 0.

Nope. The only variables that are automaticly initalized are 'static' variables, and then even with those, it's only at the time of creation, not every time the function is called.

Without you actually initializing a variable, it just hold whatever random value that bit of memory held before it was set aside for that variable.

For example:

Code:

#include <stdio.h>
int myfun1( void ) { int x; return x; }
int myfun2( void ) { int x; return x; }
int myfun3( void ) { int x; return x; }
int myfun4( void ) { int x; return x; }
int mystaticfun( void ) { int x; return x; }

int main( void )
{
    return printf("%d %d %d %d, and static: %d\n",
        myfun1(), myfun2(), myfun3(), myfun4(), mystaticfun() );
}

If any of the first 4 are zero, it's only luck or your specific compiler.

Quzah.