C programming: Basic fscanf issues with doubles

Question

I'm having some issues with fscanf. I'm very new to C but I cannot seem to get fscanf to load the correct information from a .txt file.

int main() {

    //Vars
    FILE *tempFileIn;
    int rowIndex = 0;
    int objectIdNum;
    double magnitudePhotographed;
    double distance;
    int velocity;
    double magnitudeCorrected;
    double magnitudeTotal;

    //Read File Data
    tempFileIn = fopen("hubbleData.txt","r");
    if (tempFileIn == NULL) {
        printf("File read error.");
    }

    printHeaders();
    while(!feof(tempFileIn)) {
        fscanf(tempFileIn, "%lf %lf %lf %lf %lf", &objectIdNum, &distance, &velocity, &magnitudeCorrected, &magnitudeTotal);
        printf( "%2.3f      %2.3f", velocity, distance);
        printf("\n");
        rowIndex++;
    }

    return 0;
}

The velocity is getting printed as expected but distance is always printed as 0.0000. If I switch the print order of the two, distance will be printed correctly and the velocity will be printed as 0.0000. I'm only concerned about the second and third columns but have to scan all of them as per the project guidelines.

Input format:
1      0.032    +170      1.5      -16.0
2      0.034    +290      0.5       17.2
6822   0.214    -130      9.0       12.7
598    0.263    -70       7.0       15.1
221    0.275    -185      8.8       13.4
224    0.275    -220      5.0       17.2
5457   0.45     +200      9.9       13.3

Actual Output:                
170.000      0.000
290.000      0.000
-130.000      0.000
-70.000      0.000
-185.000      0.000
-220.000      0.000
 200.000      0.000

Expected Output:
170.000      0.032
290.000      0.034
-130.000      0.214
-70.000      0.263
-185.000      0.275
-220.000      0.275
 200.000      0.45

we need to see the whole code/what you input into your program. — Dmytro
– Dmytro, Commented Mar 22, 2013 at 4:14

FatalError · Accepted Answer · 2013-03-22 04:37:17Z

2

velocity is declared int but used like a double in your fscanf() and printf() calls. You probably meant to declare it as double, too.

answered Mar 22, 2013 at 4:37

FatalError

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Comments

c.fogelklou · Accepted Answer · 2013-03-22 05:52:31Z

1

Edit: I posted this comment before the user posted the types of velocity and distance. I assumed velocity and distance were an incompatible type of float, not an integer.

Try this:

printf( "%2.3f      %2.3f", (float)velocity, (float)distance);

My guess is that you are passing variables into printf that are not the same size as floats, and so the second part of "velocity" is printed instead of distance. Printf uses the stack to pass variables and the number and size of variables are not defined by the function, so any size mismatches will cause problems like this.

edited Mar 22, 2013 at 5:52

answered Mar 22, 2013 at 4:21

c.fogelklou

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2 Comments

user2197762 Over a year ago

the float cast gives me 0's for velocity. @c.fogelklou 0.000 0.032 0.000 0.034 0.000 0.214 0.000 0.263 0.000 0.275 0.000 0.275 0.000 0.450

c.fogelklou Over a year ago

You get 0.000 for velocity because it is originally an integer in your source code. You didn't post this at first so I assumed it was a type of float. You also need velocity to be a float type, otherwise it can't hold values between 0 and 1.

999k · Accepted Answer · 2013-03-22 04:40:13Z

0

Declare objectIdNum and velocity as double so that fscanf and printf will work correctly.

you declared variable velocity as int and is using wrong format specifier in fscanf and in printf

answered Mar 22, 2013 at 4:40

999k

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Comments

Koushik Shetty · Accepted Answer · 2013-03-22 04:53:28Z

0

you need 3 changes

1) Declare velocity as double.

2) in fscanf, objectIdNum should be read as %d not %lf.

finally use flose(tempFileIn); before returning from main(exiting the program).

note: i assume velocity as double because practically velocity is a real number and not a integral value.

edited Mar 22, 2013 at 4:53

answered Mar 22, 2013 at 4:45

Koushik Shetty

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