How do I read a .csv file and save it into a 2d array?

Question

I am quite new to C programming and I have been set the task of reading a .csv file containing a 2d integer array, I need to then print it so it shows up in the terminal. The array is a 4 row by 2 col integer array, but when I use this code I get a random list of numbers. I have attached the code I used and the .csv file array and how it should look like.

#include <stdlib.h> #include <stdio.h> int main() { FILE *in_data = fopen("in.csv", "r"); int i; int j; int trIn[4][2]; if(in_data == NULL) { printf("error\n"); return 1; } for(i = 0; i < 4; i++){ for(j = 0; j < 2; j++){ char junk; if (j != 0) fgetc(in_data); fscanf(in_data, "%c%d%c", &junk, &trIn[i][j], &junk); printf("%d ", trIn[i][j]); } fgetc(in_data); printf("\n"); } return 0; }

.csv file array:

0 0 0 1 1 0 1 1

.csv file (raw):

"0","0" "0","1" "1","0" "1","1"

Mind that fgetc parses one character at a time, including spaces and newline characters. — anastaciu
– anastaciu, Commented Oct 29, 2020 at 22:41
thanks, last question: Are these numbers always a single character? — Henry Le Berre
– Henry Le Berre, Commented Oct 29, 2020 at 22:42

anastaciu · Accepted Answer · 2020-10-30 00:45:02Z

You can create a pattern which discards the unwanted characters, like so:

Live demo

for (i = 0; i < 4; i++) { for (j = 0; j < 2; j++) { //printf("%s", str); //print str to check if there are any weird chars fscanf(in_data, " \"%d\",", &trIn[i][j]); printf("%d ", trIn[i][j]); } printf("\n"); }

Chek if you have spaces in the lines after the values, that can throw fscanf off. Although a space before the specifier, like in the sample, should solve that.

Also, you can export .csv files without the quotation marks, if that's something you can control.

You can also try a more robust method using a combo of fgets and sscanf:

Live demo

char str[20]; int i = 0; int j = 0; //... while (i < 4 && fgets(str, sizeof str, in_data)) { //printf("%s", str); //print str to check if there are any weird chars if(sscanf(str, "\"%d\",\"%d\"", &trIn[i][j], &trIn[i][j+1]) == 2) printf("%d %d\n", trIn[i][j], trIn[i][j+1]); i++; }

@xmxn I added another method, if ithis doesn't work, there is something seriously wrong with your file. Perhaps nor printable characters being parsed.
fgets() followed by sscanf() (or using a pair of pointers and strtol()) is always the way to go.

Henry Le Berre · Accepted Answer · 2020-10-29 23:57:16Z

You can replace you current loop with this one:

for(i = 0; i < 4; i++){ for(j = 0; j < 2; j++){ char junk; if (j != 0) fgetc(in_data); fscanf(in_data, "%c%d%c", &junk, &trIn[i][j], &junk); printf("%d ", trIn[i][j]); } fgetc(in_data); printf("\n"); }

This works because fscanf(in_data, "%d", &trIn[i][j]) reads an int (%d) from the file in_data into the memory location of trIn[i][j]. fgetc didn't work because it only reads a single character which was then printed as if it were an integer.

EDIT: Now, for each value in the .csv file, you read to a junk variable the " and \n characters.

Line by line:

if (j != 0) fgetc(in_data); reads the , from the csv file into a junk variable (which isn't the first character on a line).

fscanf(in_data, "%c%d%c", &junk, &trIn[i][j], &junk); reads:

1st: the opening " character into a junk variable
2nd: the number (int: %d) into to memory location of trIn[i][j].
3rd: the closing " character into a junk variable

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