How to read data of different types from a csv file and store it into a 2d array

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Example of csv file:

3,4
,,C 200,
M Healing Potion:85,,M Defense:360
,,,

The first row of the file is the number of row and column, second row onwards are the data that I have to put into a 2d array. Each comma separator is a differenent column.

I am struggling to think of a way to read the data, especially with commas in between the words

What I have tried:

C++

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

/*I know I have to use structure, but I am not sure how to start*/
typedef struct{

}

int main(int argc, char *argv[])
{
FILE *map;

/*I have done declaring a 2d array with malloc*/

}

Posted 30-Apr-19 21:16pm

Member 14351155

Updated 1-May-19 5:09am

KarstenK

v2

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2 solutions

Solution 1

That's not really a CSV file - it's a set of lines of data which contain items separated by commas: a "true" CVS file contains an optional header line, then rows which contain the same number of items of the same type in each column, optionally using double quotes to delimit string values.

There's a big difference here: CSV is a table, not a "random" collection of data.

You data looks organised into rows, but the columns aren't a table - so don't call it a CSV file, call it a "configuration file" or similar because that better reflects the structure of your data. Not every row in your sample data contains four items (count the commas on the "healing potion" line for example).

Start by reading each line - which you should know how to do - and then dividing each into sections by finding the commas.

I wouldn't leap right into a structure - it's not that obvious what data types you will need from that little an example - but a 2D array is pretty trivial: read the first line and it gives you the sizes, so you can then construct a 2D array of char* . Then each separate item you find up to a comma gets copied to a new char buffer, null terminated, and set to the appropriate 2D array element.

Try it on paper and you should see what I mean.

Posted 30-Apr-19 21:39pm

OriginalGriff

Comments

OriginalGriff 1-May-19 6:36am

Start by taking a single line, and write a function that returns a pointer to an array of char* values that breaks it down into separate strings - that's pretty easy, just remember to use malloc for the whole array, and then again for each individual string as you break them up. (Hint: strcpy could be useful here!)

Test it, and make sure it works.

Member 14351155 1-May-19 6:34am

Could you please write me a short example? I am still not very sure how to do that.
I have only written the declaration of a 2D array:

char **arr;

arr = (char**)malloc(row*sizeof(char*));
for(I=0; I

Member 14351155 1-May-19 6:43am

So sorry, its difficult for me to understand by words, can I have an example?

OriginalGriff 1-May-19 6:55am

No, come on - this isn't difficult and you will learn nothing if I just give you a solution.
Write a "framework" for the method: return an array of char* pointers, accept a single char* parameter.
When you have that, show me.

Member 14351155 1-May-19 8:18am

What is mean by this sentence "Then each separate item you find up to a comma gets copied to a new char buffer, null terminated, and set to the appropriate 2D array element."?

OriginalGriff 1-May-19 8:29am

Scan the line you are handed, looking for commas.
12345,67,890
Commas at columns 5, 8

When you find one, you know how long the text is
12345,67,890
Text lengths are 5, 2, 3

Now you can allocate a chunk of memory big enough for the text plus one for the null character terminator. Malloc that (first time, 6, second 3, third 4) and add the pointer to the output array.
Then copy the text (and a null) into the new buffer.

Member 14351155 1-May-19 8:48am

For example, I have to read the first row (,,C 20,) into the array, what I need is like this, array[0][0] = nothing, array[0][1] = nothing, if detects C array[0][2] = 20, then last array[0][3] = nothing

OriginalGriff 1-May-19 10:00am

So break the task up. Start by doing it in easy stages - and the first is to break the string into separate strings. That's a "generic" task - it's independent of your data, so it can be used for the first line which contains your indexes, as well as the others.
Get that working before you move on.

Member 14351155 1-May-19 10:28am

Does that mean I have to use strtok?

OriginalGriff 1-May-19 10:32am

You certainly could.

Member 14351155 1-May-19 10:34am

Where do I have to use it? Is it in the loop where I read file and assign to the array?

Rick York 1-May-19 10:39am

The trouble with using strtok with your data is a comma is the delimiter and strtok nulls out delimiters so you will miss consecutive commas.

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Member 14351155 · Accepted Answer · 2019-05-01T05:09:00

Solution 2

char **arr;

arr = (char**)malloc(row*sizeof(char*));

for(i=0; i<row; i++)
{
arr[i] = (char*)malloc(column*sizeof(char));
}

for(i=0; i<row; i++)
for(j=0; j<column; j++)

Posted 1-May-19 5:09am

Member 14351155

Updated 1-May-19 5:10am

v2