2D Array malloc - only last Items are shown

Question

I want to malloc a 2d array and put data from a file in it. But it only shows the last items of my file. What do I have to do?

The file has 600.000 numbers like "280.000" in it.

double read_data(char *filename)
{

FILE *myFile = open_file(filename, "r");

int anzahl_zeilen = 0;
char zeile[80];

while (!feof(myFile))
{
    fgets(zeile, 80, myFile);
    anzahl_zeilen++;
}

rewind(myFile);


int i;

int **myArray = (int**)malloc(anzahl_zeilen*sizeof(int*));

for (i = 0; i < anzahl_zeilen; i++)
{
    myArray[i] = (int*)malloc(4*sizeof(double)); 
}



for (i = 0; i < anzahl_zeilen; i++)
{
    fscanf(myFile, "%lf %lf %lf %lf", &myArray[i,0], &myArray[i,1], &myArray[i,2], &myArray[i,3]);
}

printf("%lf %lf %lf %lf\n", myArray[0,0], myArray[0,1], myArray[0,2], myArray[0,3]);
printf("%lf %lf %lf %lf\n", myArray[1,0], myArray[1,1], myArray[1,2], myArray[1,3]);
printf("%lf %lf %lf %lf\n", myArray[2,0], myArray[2,1], myArray[2,2], myArray[2,3]);
printf("%lf %lf %lf %lf\n", myArray[3,0], myArray[3,1], myArray[3,2], myArray[3,3]);




return;
}

`&myArray[i,0]` That is not how 2D arrays are indexed in C. Try `&myArray[i][0]` — kaylum, Mar 20 '22 at 21:49
See [`while (!feof(file))` is always wrong!](https://stackoverflow.com/q/5431941/15168) — Jonathan Leffler, Mar 20 '22 at 22:57
Thank you very much. I have been able to understand a bit of what is in the text. — Teebow, Mar 21 '22 at 08:00

Vlad from Moscow · Accepted Answer · 2022-03-21T08:25:27.013

0

This while loop

while (!feof(myFile))
{
    fgets(zeile, 80, myFile);
    anzahl_zeilen++;
}

should be rewritten like

while ( fgets(zeile, 80, myFile))
{
    anzahl_zeilen++;
}

Also such expressions like this

&myArray[i,0]

are equivalent to

&myArray[0]

because within the square brackets there is used an expression with the comma operator. It seems you mean

&myArray[i][0]

Also the function has the return type double but returns nothing.

If you you are trying to allocate arrays of elements of the type double then in this case you need to write

double **myArray = (double**)malloc(anzahl_zeilen*sizeof(double*));

for (i = 0; i < anzahl_zeilen; i++)
{
    myArray[i] = (double*)malloc(4*sizeof(double)); 
}

And the function must have the return type double ** and return the pointer myArray.

edited Mar 21 '22 at 08:25

answered Mar 20 '22 at 22:01

Vlad from Moscow

301,070
26
186
335

I have changed the program code as far as you suggested, but now I am only reading in one line. – Teebow Mar 21 '22 at 08:15
`while (fgets(zeile, 80, myFile)); { printf("%s\n",zeile); anzahl_zeilen++; }` – Teebow Mar 21 '22 at 08:16
@Teebow You need reread the file anew. – Vlad from Moscow Mar 21 '22 at 08:16
I also replaced the commas with the [], but then the program crashes immediately. – Teebow Mar 21 '22 at 08:20
@Teebow If you allocated arrays of integers then you need to use conversion specifier %d. If you have arrays of doubles you need to use conversion specifier %lf. – Vlad from Moscow Mar 21 '22 at 08:23
These are all values of the data type Double – Teebow Mar 21 '22 at 08:34
But I dont know what you mean by "You need reread the file anew." – Teebow Mar 21 '22 at 08:35
@Teebow I mean you need correctly to use conversion specifiers. – Vlad from Moscow Mar 21 '22 at 08:39
Sorry but I really don't know what you mean by that. But I will try around. – Teebow Mar 21 '22 at 08:51

2D Array malloc - only last Items are shown

1 Answers1