fgets + dynamic malloc/realloc with a .txt as stdin - c

Question

i'm trying to read lines of a file. txt, but without knowing the size of each lines...First I used the getline instruction (and works fine), but my teacher does not let me use that instruction, he says I can only use the fgets statement with malloc and realloc...
This is an input example, with variable line sizes:
[9.3,1.2,87.9]
[1.0,1.0]
[0.0,0.0,1.0]
As shown, each line defines a different vector with no size limit
Someone could help me implement this method?
Thank you very much.
NOTE: I forgot to mention, to compile the program I use these commands:
g++ -Wall-Wextra-Werror-pedantic main.c-o metbasicos.c metintermedios.c eda.exe
./eda.exe <eda.txt

Answer 1

I would say do something similar to this
while(fgets(buf, LEN, stdin)){
z = strtok(buf, ",");
*(*(matrix + i)) = atof(z);
for(j = 1; j < col; ++j){
z = strtok(NULL, ",");
*(*(matrix + i) + j) = atof(z);
}
++i;
}
The only extra thing you would have to take care of is making sure that you strip the brackets off of the first and last element.
Of course, if you don't know the size of the final array, you might need something like this:
struct data_t {
int nval; /* current number of values in array */
int max; /* allocated number of vlaues */
char **words; /* the data array */
};
enum {INIT = 1, GROW = 2};
...
while (fgets(buf, LEN, stdin)) {
if (data->words == NULL)
data->words = malloc(sizeof(char *));
else if (data->nval > data->max) {
data->words = realloc(data->words, GROW * data->max *sizeof(char *));
data->max = GROW * data->max;
}
z = strtok(buf, "\n");
*(data->words + i) = malloc(sizeof(char) * (strlen(z) + 1));
strcpy(*(data->words + i), z);
i++;
data->nval++;
}
data->nval--;
If you combine both of those while loops into a single one, you should be all set. The first one reads in floats, the second one is good for dynamically allocating space on the fly.

Answer 2

If you can use multiple steps, then use one function to get the information you need to malloc memory. (for example determine number of lines, and longest line) This function will do that for you (given the file name and location)
[EDIT] LineCount - This function will get you the number of lines, and the longest line so you can dynamically allocate memory in char **strings; in which to read the lines of the input file.
int lineCount(char *file, int *nLines)
{
FILE *fp;
int cnt=0, longest=0, numLines=0;
char c;
fp = fopen(file, "r");
while ( (c = fgetc ( fp) ) != EOF )
{
if ( c != '\n' )
{
cnt++;
if (cnt > longest) longest = cnt;
}
else
{
numLines++;
cnt= 0;
}
}
*nLines = numLines+1;//add one more
fclose(fp);
return longest+1;
}
Here is the implementation to read the input file you provided, using the function above to get the unknown dimensions of the input file...
#include <ansi_c.h>
#include <stdio.h>
#define FILENAME "c:\\dev\\play\\in.txt" //put your own path here
#define DELIM "- ,:;//_*&[]\n" //change this line as needed for search criteria
int lineCount(char *file, int *cnt);
void allocMemory(int numStrings, int max);
void freeMemory(int numStrings);
char **strings;
int main()
{
int numLines, longest, cnt, i;
FILE *fp;
longest = lineCount(FILENAME, &numLines);
char wordKeep[longest];
allocMemory(numLines, longest);
//read file into string arrays
fp = fopen(FILENAME, "r");
cnt=0;
i=0;
for(i=0;i<numLines;i++)
{
fgets(strings[i], longest, fp);
}
fclose(fp);
freeMemory(numLines);
getchar();
return 0;
}
int lineCount(char *file, int *nLines)
{
FILE *fp;
int cnt=0, longest=0, numLines=0;
char c;
fp = fopen(file, "r");
while ( (c = fgetc ( fp) ) != EOF )
{
if ( c != '\n' )
{
cnt++;
if (cnt > longest) longest = cnt;
}
else
{
numLines++;
cnt= 0;
}
}
*nLines = numLines+1;//add one more
fclose(fp);
return longest+1;
}
void allocMemory(int numStrings, int max)
{
int i;
// need number of lines by longest line for string containers
strings = calloc(sizeof(char*)*(numStrings+1), sizeof(char*));
for(i=0;i<numStrings; i++)
{
strings[i] = calloc(sizeof(char)*max + 1, sizeof(char));
}
}
void freeMemory(int numStrings)
{
int i;
for(i=0;i<numStrings; i++)
if(strings[i]) free(strings[i]);
free(strings);
}