Returning the address of a structure - c

Question

This is the code I am working on and in the function trace* readTrace(char* fileName) I have to read a file (that fills structure) and then return the address of trace structure. Also the time and value of the structure are pointers but I don't know how to do it.
#include <stdio.h>
#include <stdlib.h>
#include <conio.h>
#include <math.h>
#define TMAX 1000
#define NBPTS 2000
#define DT 0.5
typedef struct
{
char comment[40];
int nbpts;
float time[4096];
float value[4096];
} trace;
void simuTrace(int tmax, float dt, float params[], trace *uneTrace)
{
printf("Shkruani emrin e eksperimentit : \n");
scanf("%s", &uneTrace->comment);
int i = 0;
float v = 0, w = 0, dv = 0, dw = 0, t = 0;
float a = params[0], d = params[1], e = params[2];
while (t <= tmax)
{
dv = (a - v) * (v - 1) * v - w;
dw = e * (0.5 * v - w - d);
v += dv * dt;
w += dw * dt;
uneTrace->time[i] = t;
uneTrace->value[i] = v;
i++;
t += dt;
}
uneTrace->nbpts = i;
}
void printTrace(trace uneTrace)
{
printf("%s\n", uneTrace.comment);
printf("\t%d\n", uneTrace.nbpts);
int i;
for (i = 0; i <= NBPTS; i++) {
printf(" t= %.1f \tv= %.4f \n ", uneTrace.time[i],uneTrace.value[i]);
}
}
void saveTraceBin(char *fileTrace, trace uneTrace)
{
FILE *file;
file = fopen(fileTrace, "w");
if (fopen(fileTrace, "w") == NULL) {
printf("\n Gabim! \n");
} else {
fprintf(file, "%s\n", uneTrace.comment);
fprintf(file, "%d", uneTrace.nbpts);
int i;
for (i = 0; i <= NBPTS; i++) {
fprintf(file, "\n %.1f %.4f",uneTrace.time[i],uneTrace.value[i]);
}
fclose(file);
}
}
void readTrace(char *fileName, trace *uneTrace)
{
FILE*file;
file = fopen(fileName, "r");
if (file != NULL) {
fscanf(file, "%s", uneTrace->comment);
fscanf(file, "%d", &uneTrace->nbpts);
int i;
for (i = 0; i <= NBPTS; i++) {
fscanf(file, "%f", &(uneTrace->time[i]));
fscanf(file, "%f", &(uneTrace->value[i]));
}
printf("\n Leximi perfundoi me sukses!\n");
} else {
printf("\n Gabim! \n");
}
fclose(file);
}
trace* readTrace(char* fileName) {
FILE*file;
file = fopen(fileName, "r");
if (file != NULL) {
fscanf(file, "%s", uneTrace->comment);
fscanf(file, "%d", &uneTrace->nbpts);
int i;
for (i = 0; i <= NBPTS; i++) {
fscanf(file, "%f", &(uneTrace->time[i]));
fscanf(file, "%f", &(uneTrace->value[i]));
}
printf("\n Leximi perfundoi me sukses!\n");
} else {
printf("\n Gabim! \n");
}
fclose(file);
}
float errorTrace(trace uneTrace1, trace uneTrace2)
{
float sum = 0;
int i;
for (i = 0; i <= NBPTS; i++)
{
sum += (uneTrace1.value[i] - uneTrace2.value[i]);
}
sum /= NBPTS;
return sqrt(fabs(sum));
}
int main()
{
float Pa[] = { 0.5, 0.01, 0.05 };
float Pb[] = { 0.75, 0.3, 0.1 };
float e1, e2;
trace tracePa, tracePb, traceCell;
simuTrace(NBPTS, DT, Pa, &tracePa);
printTrace(tracePa);
saveTraceBin("myfile1.txt", tracePa);
simuTrace(NBPTS, DT, Pb, &tracePb);
printTrace(tracePb);
saveTraceBin("myfile2.txt", tracePb);
readTrace("cell.txt", &traceCell);
e1 = errorTrace(traceCell, tracePa);
e2 = errorTrace(traceCell, tracePb);
printf("\n Gabimi nga llogaritja e Pa : %f ", e1);
printf("\n Gabimi nga llogaritja e Pb : %f ", e2);
if (e1 < e2)
printf("\n\n Rasti Pa eshte me i mire se rasti Pb \n");
else
printf("\n\n Rasti Pb eshte me i mire se rasti Pa \n");
return 0;
}

Answer 1

You can either return a trace* that is allocated in readTrace,
trace* readTrace(char* fileName) {
trace *tp = malloc(sizeof *tp);
if (!tp) return NULL;
// fill up tp from file
....
}
// call this in main
trace *t = readTrace("cell.txt");
free(t); // free it when done
Or you could supply trace to the function, like
void readTrace(char* filename, trace *tp) {
if (!tp) return;
// fill up tp from file
....
}
// call this in main
trace t; // define trace object
readTrace("cell.txt", &t);
As for fill up time and value, read the array from the file:
int i;
fscanf(file, "%d", &t->nbpts);
for (i = 0; i < t->nbpts; i++) {
fscanf(file, "%f", &(t->time[i]));
fscanf(file, "%f", &(t->value[i]));
}

Answer 2

The function structure should look like this
trace* readTrace(char* fileName)
{
trace* traceptr;
int no_of_elements;
// Read the no of trace elements stored in file
// Generally this is avaliable in a location in the start of file,
// If not, then you have to guess and resize if it falls short.
traceptr = malloc(sizeof(trace) * no_of_elements);
// Read the trace elements from file
return (traceptr);
}
To call it in main()
int main(void)
{
trace *traceptr;
// Other stuff
traceptr = readTrace(filename);
simuTrace(NBPTS, DT, Pa, traceptr);
}
You need to modify your printTrace function to take a pointer to struct as input instead of an entire structure. Then it can take traceptr as it's input. Similarly for the saveTraceBin function.