Write an XML file through a C program

Question

I have created a program in c to read the temperature of a specific number of days, and then save all the data inputed into an XML file. I have handled to code the program, and make it generate an XML file with the data inputed in it, however the output displayed in the XML file is wrong, it is somehow badly formatted, so I would like to know if someone could help me with it, it is the first time I am working with XML.

My code is basically this:

#include <stdio.h>
#include <stdlib.h>

typedef struct{
    double minimum;
    double maximum;
    double average;
    int daynumber;
}Measurement;

#define QUANT 31

void measure(Measurement *);
void output(FILE *, Measurement *);

int main(int argc, char** argv) {

    Measurement m[QUANT];
    int i;
    FILE *f;

    printf("Input data:\n");
    for(i=0; i<1; i++)
        measure(&m[i]);

    printf("\nData was saved into xml file\n");
    f = fopen("data.xml","w");
    if(f==NULL){
        printf("Error");
        return 0;
    }
    fprintf (f,"<?xml version=\"1.0\" encoding=\"utf-8\"?>\n");
    for(i=0;i<1;i++){
        output(f,m);
    }
    fclose(f);

    return (EXIT_SUCCESS);
}

void measure(Measurement *x){
    printf("Input minimum temperature: ");
    scanf("%f",&x->minimum);
    printf("Input maximum temperature: ");
    scanf("%f",&x->maximum);
    printf("Input average temperature: ");
    scanf("%f",&x->average);
    printf("Input day number: ");
    scanf("%f",&x->daynumber);
}
void output(FILE *f, Measurement *x){
    fprintf(f,"<day>\n");
    fprintf(f,"<minimum>%f</minimum>\n",x->minimum);
    fprintf(f,"<maximum>%f</maximum>\n",x->maximum);
    fprintf(f,"<average>%f</average>\n",x->average);
    fprintf(f,"<daynumber>%d</daynumber>\n",x->daynumber);
    fprintf(f,"</day>\n");
}

My output then is always like this:

<?xml version="1.0" encoding="utf-8"?>
<day>
  <minimum>0.000000</minimum>
  <maximum>0.000000</maximum>
  <average>0.000000</average>
  <daynumber>1065353216</daynumber>
</day>

Could you see what may be wrong in my code? Thanks in advance.

Answer 1

The problem appears to be in your function call:

 output(f,m);

This way, for each iteration, you're essentially accessing the first element m[0] in the function call.

You want to pass the address of each individual elements in the array, like

 output(f,&(m[i]));

or, to simplify, you can pass the element itself (not the address), like

 output(f,m[i]);

and change the function like

void output(FILE *f, Measurement x){ // second argument is not a pointer
    fprintf(f,"<day>\n");
    fprintf(f,"<minimum>%f</minimum>\n",x.minimum);  // x is not a pointer
    fprintf(f,"<maximum>%f</maximum>\n",x.maximum); .....

---

That said, the scan statements

  scanf("%f",&x->daynumber);

should be

  scanf("%d",&x->daynumber);

as daynumber is of type int, and for the others

scanf("%f",&x->minimum);

should be

scanf("%lf",&x->minimum);

as minimum and other members are of type double.