Remove extra white space from inside a C string?

Question

I have read a few lines of text into an array of C-strings. The lines have an arbitrary number of tab or space-delimited columns, and I am trying to figure out how to remove

Answer 1

You could read a line then scan it to find the start of each column. Then use the column data however you'd like.

#include 
#include 
#include 

#define MAX_COL 3
#define MAX_REC 512

int main (void)
{
    FILE *input;
    char record[MAX_REC + 1];
    char *scan;
    const char *recEnd;
    char *columns[MAX_COL] = { 0 };
    int colCnt;

    input = fopen("input.txt", "r");

    while (fgets(record, sizeof(record), input) != NULL)
    {
        memset(columns, 0, sizeof(columns));  // reset column start pointers

        scan = record;
        recEnd = record + strlen(record);

        for (colCnt = 0; colCnt < MAX_COL; colCnt++ )
        {
          while (scan < recEnd && isspace(*scan)) { scan++; }  // bypass whitespace
          if (scan == recEnd) { break; }
          columns[colCnt] = scan;  // save column start
          while (scan < recEnd && !isspace(*scan)) { scan++; }  // bypass column word
          *scan++ = '\0';
        }

        if (colCnt > 0)
        {
            printf("%s", columns[0]);
            for (int i = 1; i < colCnt; i++)
            {
             printf("#%s", columns[i]);
            }
            printf("\n");
        }
    }

    fclose(input);
}

Note, the code could still use some robust-ification: check for file errors w/ferror; ensure eof was hit w/feof; ensure entire record (all column data) was processed. It could also be made more flexible by using a linked list instead of a fixed array and could be modified to not assume each column only contains a single word (as long as the columns are delimited by a specific character).