How to fill array with elements in a .txt file - c

Question

I have a dynamic 2D float array and a file with both strings, integers(number of floats in the line) and float numbers.
M = (float**)malloc(num_lines * sizeof(float));
for(int i = 0; i < num_lines; i++){
M[i] = (float*)malloc(num_columns * sizeof(float));
}
Example:
2
John 3 5.5 89.5 30.67 0.00
Mary 4 78.9 67.4 67.3 9.0 0.00
(null)
The number of lines is the one on the file + 1 and the number of columns is the highest integer + 1 (5 in this case) because the 0.00 marks the end of each line.
How do I load only the floats into memory? I've tried different types of loops with fgets and strtok but it doesn't work due to the different types of variables.
The code is like this:
for(int i = 0; i < num_lines; i++){
fgets(buf, 1000, aux);
name = strtok(buf, " ");
col = atoi(strtok(NULL, " "));
for(j = 0; j < num_columns; j++){
M[i][j] = atof(strtok(NULL, " "));
if(M[i][j] == 0.00){
break;
}
}
}

Answer 1

This sort of parsing is a bit of a pain, but is a good exercise to do every now and again. This is relatively easy with scanf, but scanf is not suitable for anything but toys. (It is literally impossible to correctly handle anything robustly, since even a simple "%d" format specifier leads to undefined behavior on certain input.) Unless you are willing to read the file twice to determine the maximum size of a column, you can't preallocate the entire array. Instead of that, I would suggest doing something like:
#include <ctype.h>
#include <err.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
/* sample input
2
John 3 5.5 89.5 30.67 0.00
Mary 4 78.9 67.4 67.3 9.0 0.00
*/
FILE * xfopen(const char *, const char *);
void * xmalloc(size_t);
int get_row_count(FILE *in, char **line, size_t *cap, const char *name);
float * parse_line(const char *s, int lc);
int
main(int argc, char **argv)
{
int lc = 0;
char *line = NULL;
size_t cap = 0;
FILE *in = argc > 1 ? xfopen(argv[1], "r") : stdin;
int rows = get_row_count(in, &line, &cap, argv[1]);
float **M = xmalloc(rows * sizeof *M);
for( lc = 0; lc < rows && getline(&line, &cap, in) > 0; lc += 1 ){
M[lc] = parse_line(line, lc + 1);
}
if( lc != rows ){
warnx("invalid input: missing some rows");
}
for( int i = 0; i < lc; i++ ){
float *f = M[i];
for( int j = 0; j < f[0]; j++ ){
printf("%f\t", f[j + 1]);
}
putchar('\n');
}
}
float *
parse_line(const char *s, int lc)
{
/* Skip the name */
char *end;
while( *s && ! isspace(*s) ){
s += 1;
}
int siz = strtol(s, &end, 10);
if( siz <= 0 || ! isspace(*end) ){
errx(EXIT_FAILURE, "Invalid input on line %d", lc);
}
float *f = xmalloc((1 + siz) * sizeof *f);
f[0] = siz;
for( int i = 1; i < siz + 1; i += 1 ){
f[i] = strtof(end, &end);
}
while( isspace(*end) ){
end += 1;
}
if( *end == '\0' || strcmp(end, "0.00\n") ){
errx(EXIT_FAILURE, "Invalid input on line %d", lc);
}
return f;
}
int
get_row_count(FILE *in, char **line, size_t *cap, const char *name)
{
if( getline(line, cap, in) <= 0 ){
if( feof(in) ){
errx(EXIT_FAILURE, "Empty input");
} else {
err(EXIT_FAILURE, "%s", name);
}
}
char *end;
int rows = strtol(*line, &end, 10);
if( rows <= 0 ){
errx(EXIT_FAILURE, "invalid row count: %d", rows);
}
if( *end != '\n' ){
errx(EXIT_FAILURE, "unexpected input on line 1");
}
return rows;
}
FILE *
xfopen(const char *path, const char *mode)
{
FILE *fp = path[0] != '-' || path[1] != '\0' ? fopen(path, mode) :
*mode == 'r' ? stdin : stdout;
if( fp == NULL ){
perror(path);
exit(EXIT_FAILURE);
}
return fp;
}
void *
xmalloc(size_t s)
{
void *rv = malloc(s);
if( rv == NULL ){
perror("malloc");
exit(EXIT_FAILURE);
}
return rv;
}