Extracting data from input file? - c

Question

I've been stuck on this problem for a while.
I'm creating a program that that reads in an input file (just a plain .Txt) This input file stores variables in the following format:
x
21
% This is a comment
y
3
And so on. My goal is to read this input file (done), and then store every variable in the file into a global variable in my c program. I.e. Global variable x will have the value 21 and y will have the value 3 in my c file, whilst comments are ignored.
I've thought about this for a while and can't figure out what functions to use. Any suggestions would be appreciated, thanks.
(note that these variables will always have the same names, but the order in which they are presented will differ from input file to input file).

Answer 1

I would suggest you to have a struct with two fields.
struct Foo
{
char var_name;
int var_value;
};
Then you create an array of these structs, with the size of the expected variables in your input file.
struct Foo input_array[n];
Then, as you read your file, you set the struct fields...
for(int i = 0; i < n ; i++){
input_array[i].var_name = input_var_name;
input_array[i].var_value = input_var_value;
}
Afterwards you print the values, and they will already be in order.

Answer 2

First of all, we need the variables to read the values into:
int x, y, z /* etc */;
Now, lets make an array of pointers so that we can easily access the variables:
int *array[] = { &x, &y, &z /* etc */ };
Now, we need a FILE* to access the file:
FILE* fp;
Opening the file:
fp = fopen("filename.txt", "r"); /* 'r' for reading */
Checking if the file opened successfully:
if(fp == NULL)
{
printf("Error opening file");
exit(-1); /* Exit the program */
}
Now, reading the file using fscanf:
int counter = 0; /* For keeping track of the array index */
for(;;) { /* Infinite loop */
int retVal = fscanf(fp, "%d", array[counter]); /* Capture return value of fscanf */
if(retVal == 1) /* Successfully scanned a number */
{
counter++;
}
else if(retVal == 0) /* Failed to scan a number */
{
fscanf(fp, "%*s"); /* Discard a word from the file */
}
else /* EOF */
{
break; /* Get out of the loop */
}
}
Now, printing the scanned data:
int i;
for(i = 0; i < counter; i++)
printf("%d", *array[i]);
and finally, closing the file:
fclose(fp);
Full code, added with #Jongware's suggestions:
int x, y, z /* etc */;
int *array[] = { &x, &y, &z /* etc */ };
char line[1024];
const char *varNames[] = { "x", "y", "z" };
int tmp = -1;
FILE* fp;
fp = fopen("filename.txt", "r"); /* 'r' for reading */
if(fp == NULL)
{
printf("Error opening file");
exit(-1); /* Exit the program */
}
int counter = 0;
for(fgets(line, sizeof(line), stdin)) {
if(line[0] == '%')
continue;
else
{
tmp = -1;
for(int i = 0; i < sizeof(varNames) / sizeof(*varNames); i++)
{
if(strcmp(line, varNames[i]) == 0)
{
tmp = i;
break;
}
}
fgets(line, sizeof(line), stdin);
sscanf(line, "%d", array[tmp]);
}
}
int i;
for(i = 0; i < counter; i++)
printf("%d", *array[i]);
fclose(fp);
All the above code is untested