Count how many integers are in the text file using fscanf - c

Question

For example, I have a txt file with all integers. I want to count how many integers there are in order to allocate an array.
int array[0];
int count = 0;
FILE *file = fopen("file1.txt","r");
while(fscanf(file,"%d",&array[count])==1){
count++;
}
printf("%d",count);
Currently there are error messages and won't go through. Is this the way fscanf work?

Answer 1

You cannot create an array of size 0. If you want to only count the number of integers, don't use an array, but only a temporary variable.
It is a good idea to check whether you opened the file correctly and to close the file too.
#include <stdio.h>
int main(){
int temp;
int count = 0;
FILE *file = fopen("file1.txt","r");
if(file == NULL){
printf("Could not open specified file");
return -1;
}
while(fscanf(file,"%d",&temp)==1){
count++;
}
fclose(file);
printf("%d",count);
}
return 0;
}
If you also want to store the values for later use, you could for example read through the file twice, first time counting the amount of integers, then using this amount to declare the needed array. An important thing before the second run is to rewind the file pointer, to read the file from the start.
#include <stdio.h>
int main(){
int temp;
int count = 0;
FILE *file = fopen("file1.txt","r");
if(file == NULL){
printf("Could not open specified file");
return -1;
}
while(fscanf(file,"%d",&temp)==1){
count++;
}
printf("%d",count);
if(count == 0){ //do not create array of size 0
fclose(file);
}
else{
//second run
int array[count];
rewind(file);
for(int i=0; i<count; i++){
fscanf(file,"%d",&array[count]);
}
fclose(file);
//continue using array...
}
return 0;
}

Answer 2

int array[0];
and
fscanf(file,"%d",&array[count])
will lead to a segmentation fault because you're accessing the array out of bounds.
If you need flexible array you need
int *array
a place-holder for storing each number from fscanf
realloc array every time you find a new number and add the number to array.

Answer 3

#include <stdio.h>
#define isDigit(c) ('0' <= (c) && (c) <= '9') ? 1 : 0
int main() {
FILE *fd;
int counter, c, tmp;
if ((fd = fopen("PathToFile", "r")) != NULL){
do{
c = getc(fd);
if (isDigit(c)) tmp = 1;
else if (tmp == 1 && !isDigit(c)){
counter++, tmp = 0;
}
}while (c != EOF);
}else{
printf("Couldn't find File!");
return 1;
}
fclose(fd);
printf("%i", counter);
return 0;
}