Get value from a CSV table in C

Question

I have made a matrix in MatLab and exported it as a CSV. I don't really know how to use it in my C code though. For example, my table looks like this (allthough much bigger and more complicated values):

Height/Angle, 50, 550, 1050, 1550, 2050
5, 0.9, 0.8, 0.7, 0.6, 0.5
6, 0.8, 0.7, 0.6, 0.5, 0.4
7, 0.7, 0.6, 0.5, 0.4, 0.3
8, 0.6, 0.5, 0.4, 0.3, 0.2
9, 0.5, 0.4, 0.3, 0.2, 0.1

So what I want is a function that takes two arguments and returns the corresponding value from the table. I have a program that gives me the height and the angle of a plane, seen from an IR-sensor, and given those values I want the corresponding value. For example: GetValueFromCSV(550,7); should return 0.6 in my example. But I have no idea how to do this. I have done some research with ´strtok()`, but that doesn't really seem like what I need. Please help out a noob.

Answer 1

. o O ( yes, code-only answer cause code is quite self-explanatory )

#include <stddef.h>
#include <stdbool.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

typedef struct row_tag
{
    int index;
    double *data;
} row_t;

size_t get_col_count(FILE *is)
{
    size_t col_count = 1;

    int ch;
    while ((ch = fgetc(is)) != EOF && ch != '\n')
        if (ch == ',')
            ++col_count;

    rewind(is);
    return col_count;
}

row_t* csv_read(FILE *is, size_t *cols, size_t *rows)
{
    *cols = get_col_count(is);
    *rows = 0;
    char const *origin_format = "%*[^ ,]%c";
    char const *row_header_format = "%d%c";
    char const *format = "%lf%c";
    row_t *csv = NULL;

    bool valid = true;
    for (size_t current_row = 0; valid; ++current_row) {
        csv = realloc(csv, (current_row + 1)* sizeof(row_t));
        csv[current_row].data = calloc(cols - 1, sizeof(double));

        for (size_t current_col = 0; valid && current_col < cols; ++current_col) {

            char delim;
            if (!current_col && !current_row) {
                if (fscanf(is, origin_format, &delim) != 1 || delim != ',') {
                    valid = false;
                    continue;
                }
                csv[0].index = -1;
            }
            else if (!current_col) {
                int result = -1;
                if ((result = fscanf(is, row_header_format, &csv[current_row].index, &delim)) != 2 || delim != ',') {
                    valid = false;
                    continue;
                }
            }
            else {
                if (fscanf(is, format, &csv[current_row].data[current_col - 1], &delim) != 2 || delim != ',' && delim != '\n')
                    valid = false;
            }
        }

        if (!valid)
            free(csv[current_row].data);
        else *rows = current_row + 1;
    }

    return csv;
}

void csv_free(row_t *csv, size_t rows)
{
    for (size_t row = 0; row < rows; ++row)
        free(csv[row].data);
    free(csv);
}

double csv_get_value(row_t *csv, int col_index, size_t cols, int row_index, size_t rows)
{
    size_t col;
    for (col = 1; csv[0].data[col] != col_index && col < cols; ++col);
    if (col >= cols || csv[0].data[col] != col_index)
        return 0.;

    size_t row;
    for (row = 1; csv[row].index != row_index && row < rows; ++row);
    if (row >= rows || csv[row].index != row_index)
        return 0.;

    return csv[row].data[col];
}

int main(void)
{
    char const *filename = "test.txt";
    FILE *is = fopen(filename, "r");
    if (!is) {
        fprintf(stderr, "Couldn't open \"%s\" for reading!\n\n", filename);
        return EXIT_FAILURE;
    }

    size_t cols;
    size_t rows;
    row_t *csv = csv_read(is, &cols, &rows);
    printf("Cols: %zu\nRows: %zu\n\n", cols, rows);

    fclose(is);

    // have fun with csv:
    for (size_t y = 0; y < rows; ++y) {
        printf("%2d: ", csv[y].index);
        for (size_t x = 0; x < cols - 1; ++x)
            printf("%f ", csv[y].data[x]);
        putchar('\n');
    }

    double value = csv_get_value(csv, 550, cols, 7, rows);
    printf("\n%f\n", value);


    csv_free(csv, rows);
}

Output:

Cols: 6
Rows: 6

-1: 50.000000 550.000000 1050.000000 1550.000000 2050.000000
 5: 0.900000 0.800000 0.700000 0.600000 0.500000
 6: 0.800000 0.700000 0.600000 0.500000 0.400000
 7: 0.700000 0.600000 0.500000 0.400000 0.300000
 8: 0.600000 0.500000 0.400000 0.300000 0.200000
 9: 0.500000 0.400000 0.300000 0.200000 0.100000

0.600000