Formatting text file into columns with sprintf with C - c

Question

I have a basic text file I point my program at to run that has numbers line by line such as:
3
30
300
3000
30000
300000
3000000
30000000
300000000
-3
-30
-300
-3000
-30000
-300000
-3000000
-30000000
-300000000
and I need to print them out into evenly spaced columns and I want them to fit into 40 characters (4 columns wide). I want to use the sprintf function to do this. So basically print each number out plus 2 spaces for formatting and fit within 40 characters total. So far this is what I have.
int main(int argc, char *argv[]){
int a, b, num[1000], nums = 0;
char str[40];
FILE *pt;
int col, max, w;
if(argc < 2){
printf("Usage %s <No Files>\n", argv[0]);
return 1;
}
if((pt = fopen(argv[1], "r")) == NULL){
printf("Unable to open %s for reading.\n", argv[1]);
return 1;
}
while(fscanf(pt, "%d", &b) == 1){
num[nums++] = b;
}
w = sprintf(str, "%*d", num[a]);
if(max < w){
col = 40 / (max + 2);
printf("%d %d\n", w, num[a]);
}
return 0;
}
I just get garbage when I point it to the text file mentioned in the above. Any advice?

Answer 1

To print N numbers in 4 columns with width 10 characters use printf("%10d") inside the loop that add new line (\n) after each 4th printing, e.g.:
for (int i = 1; i <= nums; i++)
{
printf("%10d", num[i-1]); // or printf("%-10d", num[i-1]);
if (i % 4 == 0)
printf("\n"); // or putchar ('\n')
}
sign - in the format %-10d change alignment.
As you see sprinf is not used here, I use printf for each number to print the value at screen (standard output).
UPDATE:
If you want to find optimal width of the column, and use it for output, e.g. using the number of digits in your biggest number (let it be maxValue an integer value found in the array num), you can find the minimum required number of digits (let it be minWidth), like:
char buff[20] = {0};
int minWidth = strlen(_itoa(maxValue,buff,10));
and then change the printing loop like:
for (int i = 1; i <= nums; i++)
{
printf("%*d", minWidth + 1, num[i - 1]);
if (i % 4 == 0) putchar('\n');
}
here vlaue minWidth + 1 will be used in format specifier %*d instead of *, and +1 is used for minimum separation between columns in one space (of course, there can be 2 or 3).
Finally, having the column width calculated, you can find the number of column for your screen and use this value for starting new line, e.g.:
const int screenWidth = 80;
int colWidth = minWidth + 2; // here 2 is added for minimum separation of columns
int colNum = screenWidth / colWidth;
for (int i = 1; i <= nums; i++)
{
printf("%*d", colWidth, num[i - 1]);
if ( !(i % colNum) ) putchar('\n'); // !(i % colNum) is the same to i % colNum == 0
}

Answer 2

This is my second answer for the same question, but this answer more close to the topic - here output is made to the string with sprintf.
So, lets we have array of numbers int num[1000] and we need to print nums of them to several string (length is limited by value stringMaxLength) using formatting as columns with width depending on length of number representation (maximum number in the array).
The following snippet has comments for all operations
// string that will be made from numbers
const int stringMaxLength = 120;
char str[stringMaxLength + 1]; // just one string
// find longest number considering sign
char buff[20] = { 0 };
int maxNumWidth = 0, numWidth;
int n;
for (n = 0; n < nums; n++)
{
numWidth = strlen(_itoa(num[n], buff, 10));
if (numWidth > maxNumWidth)
maxNumWidth = numWidth;
}
int colWidth = maxNumWidth + 1; // a column size with one space between columns
int colNum = stringMaxLength / colWidth; // number of columns in one string
int s, i; // i - nums counter, s - strings counter
for (i = 0, s = 1; i < nums; s++) // loop counts strings but with condition for nums
{
int sizeCnt = 0; // start making new string str
// loop works while there are numbers and the line is not filled completely
while (i < nums)
{
// add next number (column) to the string and increase string size
sizeCnt += sprintf(str + sizeCnt, "%*d", colWidth, num[i++]);
if (i % colNum == 0) // if string has colNum numbers it is full
{
break; // stop while loop
}
}
// next string is ready and can be used
printf("%d : %s\n", s, str); // e.g. for output
}