sscanf not scanning in the elements from string properly - c

Question

I have created the following program
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <string.h>
const double PI = 3.14159;
int main()
{
char str[120];
double distance, azimuth;
double delta_x = 0;
double delta_y = 0;
FILE *fp = fopen("input.txt", "r");
if (fp == NULL)
return -1;
fgets(str, sizeof(str), fp); //skip first line
while (fgets(str, sizeof(str), fp)) {
if (strcmp("Dig here!", str) == 0)
break;
printf(str);
sscanf(str, "go %f feet by azimuth %f\n", &distance, &azimuth);
printf("distance %f azimuth %f\n", distance, azimuth);
delta_y += distance * sin(azimuth * (PI/180));
delta_x += distance * cos(azimuth * (PI/180));
}
printf("%d %d", delta_x, delta_y);
fclose(fp);
return 0;
}
input.txt looks something like this
Stand at the pole with the plaque START
go 500 feet by azimuth 296
go 460 feet by azimuth 11
Dig here!
However the output gives
go 500 feet by azimuth 296
distance 0.000000 azimuth 0.000000
I'm sure it's a dumb error I am missing but I can't seem to find it, any help would be appreciated.

Answer 1

The "%f" format specifier of scanf is for float type:
f – Matches an optionally signed floating-point number; the next pointer must be a pointer to float.
If you wish to parse a double type then use the l format specifier in combination with f:
l – Indicates either that the conversion will be one of d, i, o, u, x, X, or n and the next pointer is a pointer to a long int or unsigned long int (rather than int), or that the conversion will be one of e, f, or g and the next pointer is a pointer to double (rather than float).
So, you should change your format string as follows:
sscanf(str, "go %lf feet by azimuth %lf\n", &distance, &azimuth);
printf("distance %lf azimuth %lf\n", distance, azimuth);
Note that fgets may contain trailing '\n', in other words if a newline is read, it is stored into the buffer. Therefore before you compare the input coming from fgets against "Dig here!", you have to remove the newline first.
There is many options to do this, in the comments below you can see a good one or you can use the following approach with strcspn function:
str[strcspn(str, "\r\n")] = '\0'; /* works for any combination of CR and LF */
if(strcmp("Dig here!", str) == 0)
break;