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Apr 19th, 2007

Reading in data into array (special case, please see)

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Hi there,
I need to make a piece of code in C that
1. opens a specified file,
2. Reads the data in the file and separates it as shown below,
3. Converts the strings into integers and then perfoms some manipulation on them,
4. returns the new values to a second text file (possibly, not quite sure on this one yet).
My data is given in the following format (there is one space between a1 and b1, b1 and c1, etc.):
x
y
a1 b1 c1 d1 e1 f1
a2 b2 c2 d2 e2 f2
while not EOF
I would like to read in data in the following format for further processing:
x
y
a[i] b[i] c[i] d[i] e[i] f[i]
a[i+1] b[i+1] c[i+1] d[i+1] e[i+1] f[i+1]
I guess I need to read it in as an array and then do some sort of concatenation/speration (my inputs can be one or two digits, i.e. a[i] can be 0 or 99). This is probably not very difficult, but I haven't touched C in about 6-7 years. It must be done in C (no C++ or C#). I tried to search, but couldn't find my case (maybe it was posted before and I just did not see it).

Please give me some hints. Timewise, I should be able to have it working ASAP.

Thank You very much.

Last edited by Rob111; Apr 19th, 2007 at 11:47 pm.

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Rob111

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Apr 20th, 2007

Re: Reading in data into array (special case, please see)

not clear what a1 b1 c1 ... represents.

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Apr 20th, 2007

Re: Reading in data into array (special case, please see)

Click to Expand / Collapse Quote originally posted by Ancient Dragon ...

not clear what a1 b1 c1 ... represents.

a1 b1 c1 are integers, which can vary between 0 and 99.

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Apr 20th, 2007

Re: Reading in data into array (special case, please see)

first, create the arrays of appropriate size. If you know the number of rows and columns in the file it will make it a lot easier. But if you don't (and normally you will not) then you will just have to dynamically allocate them with malloc().

Easiest way is to put it into one large array

c Syntax (Toggle Plain Text)
// array to be allocated
int *array = 0;
int x = 0;
int y = 0;
 
// open the file for reading
FILE* fp = fopen("file","r");
// read x and y
fscanf(fp,"%d", &x);
fscanf(fp,"%d", &y);
 
// allocate the array
array = (int *)malloc(y * x * sizeof(int));
 
// read the data into the arra
int i = 0;
int maxi = x * y;
for(i = 0; i < maxi && fscanf(fp,"%d", array[i]) > 0; i++)
         ;
fclose(fp);
// array to be allocated
int *array = 0;
int x = 0;
int y = 0;

// open the file for reading
FILE* fp = fopen("file","r");
// read x and y
fscanf(fp,"%d", &x);
fscanf(fp,"%d", &y);

// allocate the array
array = (int *)malloc(y * x * sizeof(int));

// read the data into the arra
int i = 0;
int maxi = x * y;
for(i = 0; i < maxi && fscanf(fp,"%d", array[i]) > 0; i++)
         ;
fclose(fp);

// now you can calculate the location of any x,y cell by this simple formula

C++ Syntax (Toggle Plain Text)
int row = 5; // desired row
int col = 3;  // desired column
int cell = (<desired row number>-1) * <columns per row> ) + (<desired column number>)
or
cell = ((row-1) * x) + col;
int row = 5; // desired row
int col = 3;  // desired column
int cell = (<desired row number>-1) * <columns per row> ) + (<desired column number>)
or
cell = ((row-1) * x) + col;

Last edited by Ancient Dragon; Apr 20th, 2007 at 10:09 am.

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Apr 20th, 2007

Re: Reading in data into array (special case, please see)

Thanks Ancient Dragon,

I probably was not very clear on the task, so here are clarifications:
- x & y have no impact on the # of rows and columns
-I do not know the number of rows in the file and the number of rows will vary from file to file
-there are always 6 elements in a row (or line), but number of digits in each element can be 1 or 2 (i.e. a1 can vary from 0 to 99); the elements (columns) are separated by one space
-I would like to sort data into array as speficied in original post, I believe it will make the analysis better: I can just increment I to perform manipulations with the next row of data.

Thanks again.

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Apr 20th, 2007

Re: Reading in data into array (special case, please see)

so use realloc() to expand the 2d array to the desired size. Something like this untested code

c Syntax (Toggle Plain Text)
// allocate first row
int **array = malloc( sizeof(int*) );
// allocate 6 columns
array[0] = malloc( 6 * sizeof(int));
int numRows = 0;
int n;
int row = 0;
int col = 0;
while( fread(fp,"%d", &n) > 0)
{
    if( col < 6)
    {
       array[row][col] = n;
       ++col;
    }
    else
    {
       ++row;
       array = realloc(array,row * sizeof(int*));
       array[row] = malloc( 6 * sizeof(int));
       col = 0;
       array[row][col] = n;
       ++col;
     }
 }
// allocate first row
int **array = malloc( sizeof(int*) );
// allocate 6 columns
array[0] = malloc( 6 * sizeof(int));
int numRows = 0;
int n;
int row = 0;
int col = 0;
while( fread(fp,"%d", &n) > 0)
{
    if( col < 6)
    {
       array[row][col] = n;
       ++col;
    }
    else
    {
       ++row;
       array = realloc(array,row * sizeof(int*));
       array[row] = malloc( 6 * sizeof(int));
       col = 0;
       array[row][col] = n;
       ++col;
     }
 }

Last edited by Ancient Dragon; Apr 20th, 2007 at 11:52 pm.

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Apr 21st, 2007

Re: Reading in data into array (special case, please see)

Getting the following error:

Error c:\lcc\projects\reading\reading.c: 23 type error in argument 2 to `fread'; found 'pointer to char' expected 'unsigned int'
Error c:\lcc\projects\reading\reading.c: 23 type error in argument 3 to `fread'; found 'pointer to int' expected 'unsigned int'
Error c:\lcc\projects\reading\reading.c: 23 insufficient number of arguments to `fread'

for the following line: while( fread(fp,"%d", &n) > 0)

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Apr 22nd, 2007

Re: Reading in data into array (special case, please see)

I got it, you meant fscanf innstead of fread. It works. Thank you very much, Ancient Dragon.

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