Convert gnuplot-like text data to wave format.

wavwriter.c

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

#define ROW_SIZE 1024

char header[44] = {
    'R', 'I', 'F', 'F',
    0, 0, 0, 0,
    'W', 'A', 'V', 'E',
    'f', 'm', 't', ' ',
    0x10, 0, 0, 0,
    1, 0,
    1, 0,
    0x44, 0xAC, 0, 0,
    0x44, 0xAC, 0, 0,
    0x01, 0,
    0x08, 0,
    'd', 'a', 't', 'a',
    0, 0, 0, 0
};


int main(int argc, char *argv[])
{
    FILE *input, *output;
    int col;
    double freq, max;
    char row[ROW_SIZE];
    int i;
    int count, rate, written, size;
    char *index, *next;
    double data;

    if (argc-1 < 5)
    {
        perror("Usage: wavwriter <input> <output> <column number> <max value> <frequency>");
        exit(EXIT_FAILURE);
    }

    col  = atoi(argv[3]);
    max  = atof(argv[4]);
    freq = atof(argv[5]);
    rate = (int)(freq / 44100 + 0.5);

    input = fopen(argv[1], "r");
    if (input == NULL)
    {
        perror(argv[1]);
        exit(EXIT_FAILURE);
    }
    output = fopen(argv[2], "w");
    if (output == NULL)
    {
        perror(argv[2]);
        exit(EXIT_FAILURE);
    }

    fwrite(header, sizeof(char), sizeof(header) / sizeof(char), output);
    count = 
    written = 0;
    while (fgets(row, ROW_SIZE, input))
    {
    if (row[0] > '9')
		continue;

        index = row;
        for (i = 1; i < col; i++)
        {
            index = strchr(index, ' ');
            if (index == NULL)
                goto TAIL;
            while (index[0] == ' ')
                index++;
        }

        next = strchr(index, ' ');
        if (next != NULL)
            *next = '\0';

        data += atof(index);
        count++;
        if (count == rate)
        {
            fputc((char)((data / rate / (2. * max) + 0.5) * (1 << 8)), output);
            data = 0;
            count = 0;
            written++;
        }

    TAIL: ;
    }

    fseek(output, 4, SEEK_SET);
    size = written + 36;
    fputc(size & 0xFF, output);
    fputc((size >>  8) & 0xFF, output);
    fputc((size >> 16) & 0xFF, output);
    fputc((size >> 24), output);

    fseek(output, 40, SEEK_SET);
    size = written;
    fputc(size & 0xFF, output);
    fputc((size >>  8) & 0xFF, output);
    fputc((size >> 16) & 0xFF, output);
    fputc((size >> 24), output);

    if (output == NULL)
    {
        perror(argv[2]);
        exit(EXIT_FAILURE);
    }
    
    fclose(output);
    fclose(input);

    return EXIT_SUCCESS;
}