Input numbers from Stdin [duplicate] - c

Question

This question already has an answer here:
How to use sscanf in loops?
(1 answer)
Closed 1 year ago.
I was trying to create a AVLtree using stdin input in C, the format I was trying to in put is: (7,19) (5,16) (9,13). The code I am using is
char str[1024];
int key,value;
while (fgets(str,256,stdin)!=NULL)//stop read files when reached end of the line
{
if(*str == "\n")
{
break;
}
if(sscanf(str,"(%d, %d)",&key, &value) == 2)// if the function can address both number
{
//InsertNode(AVLtree,key,value);
printf("%d, %d\n", key,value);
}
else
{
printf("cannot get correct key & Value");
exit(1)
}
Basically, I am saying that read input from stdin using "fgets" function, in (%d, %d) format. Once it reached the end of the line, then stop. But by using this code, it only allows me to type in those nodes one per line, instead of typing all of them and end with enter. Is there any way to fix this?

Answer 1

As you don't know how many value pairs the user will enter you have to use a loop.
After a successful sscanf you can search for a closing parenthesis ')' and start the next sscanf from the position after it.
To avoid an error message in case of additional spaces between or after the data I added code to skip whitespace and changed the format string to be more flexible.
I use a function for skipping space and checki9ng for end-of-string because I need it at two places.
Edit:
As shown in the answer to a similar question How to use sscanf in loops? you can get the offset to the next position directly from sscanf using the %n format specifier, so the strchr is not necessary. I won't change this answer here. See the other question and adapt the code accordingly.
(There are more ways to solve this problem.)
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
/* skip whitespace and check for end of string */
int skip_space(char **pos)
{
while(isspace(**pos))
{
(*pos)++;
}
return (**pos == '\0');
}
int main()
{
char str[1024];
char *pos;
int key,value;
printf("enter key-value pairs of integer numbers like (a,b)(c,d): ");
while (fgets(str,sizeof(str),stdin)!=NULL)//stop read files when reached end of the line
{
pos = str;
if(skip_space(&pos))
{
break;
}
do
{
/* added spaces to format string for more flexibility */
if(sscanf(pos," (%d , %d )",&key, &value) == 2)// if the function can address both number
{
//InsertNode(AVLtree,key,value);
printf("%d, %d\n", key,value);
}
else
{
printf("cannot get correct key & Value at position %d: %s\n", (int)(pos - str), pos);
exit(1);
}
/* since scanf was successful we must have a ')' in the input, so NULL should not occur */
pos = strchr(pos, ')');
/* skip ')' */
pos++;
} while(skip_space(&pos) == 0);
}
return 0;
}
Result:
enter key-value pairs of integer numbers like (a,b)(c,d): (1,2) ( 3 , 4 ) (5,6)(7.0,8)
1, 2
3, 4
5, 6
cannot get correct key & Value at position 21: (7.0,8)
enter key-value pairs of integer numbers like (a,b)(c,d): (1,2) ( 3 , 4 ) (5,6)
1, 2
3, 4
5, 6
(7,8)
7, 8
Unrelated error: if(*str == "\n") is wrong.
If you want to check for a newline character at the beginning of the string, use
if(*str == '\n')
If you want to check if the whole string is equal to a string that consists of a single newline, use
if(strcmp(str, "\n") == 0)
or simplified
if(!strcmp(str, "\n"))