Thread: entering string variable size

char * fgets(char * buffer, int max_len, FILE * stream);

For console input, the 'stream' would be 'stdin'.

[edit]
Just reread your post...
make sure the pointer you are using points to valid memory!
[/edit]

>I' m wondering if this is a good way to get string from user
Not at all, string points to an indeterminate address and gets doesn't restrict the user from entering more data than you can handle. For reading a line, use fgets.

>but then I'll have fixed size of string
You have two options: Use a fixed length array as the upper limit of the string size, or use malloc and friends to maintain an arbitrary length string. The former is simpler, the latter is more flexible.

> How can I know size when expecting user to enter string from keyboard?
You can't.

You always have to read from stdin using fgets() into some fixed sized buffer. If the user decides to type in a lot, then you can start calling memory allocation routines to save each fragment in say a linked list.

Code:

char buff[BUFSIZ];
while ( fgets( buff, sizeof buff, stdin ) != NULL ) {
    char *p = strchr( buff, '\n' );  /* find the newline */
    if ( p == NULL ) {
        /* no newline, user filled the buffer */
        /* copy this buff to allocated memory and */
        /* repeat calls to fgets() */
    } else {
        /* do something with buff */
        /* and/or the allocated memory containing partial input */
    }
}

Originally posted by Micko
I'm making program that asks user to enter some string. I use char *string;
gets(string);
I' m wondering if this is a good way to get string from user and if there is possibility that user enter string so big to overwrite some other later data in my program and cause run-time error, because string is pointer to first byte of data.
one of the possible solution is
char string[80];
this will force compiler to set aside memory but then I'll have fixed size of string.
Thank you

Forget the malloc
Forget the linked list
The only way to read in a string at your level of knowledge is to use fgets() as suggested and specify a char string[MX];
where MX is the maximum size of your potential input. If you're worried about someone typing too much, make MX = 2048 -- there ain't nobody gonna type that many characters from the keyboard.

All normal string input must go into a pre-defined buffer unless you are at a level of skill to deal with dynamic buffers, direct character input, etc. Learn the basics first.

Originally posted by Salem
You always have to read from stdin using fgets() into some fixed sized buffer. If the user decides to type in a lot, then you can start calling memory allocation routines to save each fragment in say a linked list.

fgetc doesn't exist any more? No one said it had to be efficient.

Quzah.