Separately scanning a sentence and number(s) in C

Question

Let's say I have a text file (hw.dat) that lists data (name, height(cm), weight(kg)):

Yuri            164     80 
Lai San Young   155     60
John Wayne      180     93

and the list continues.

I'd like to scan and print all of the data in this format:

name: Yuri, height: 164, weight: 80
name: Lai San Young, height: 155, weight: 60

and so on.

Here is my failed attempt (code segments). I intended to write code that reads the hw.dat file line by line while printing out the data line by line:

double h, w;
char name[100];

FILE *fr;
fr = fopen ("hw.dat", "r");

while (fscanf(fr,"%[^\n]s %lf %lf", name, &h, &w)!=EOF)
{
    printf ("name: %s, height: %lf, weight: %lf \n", name, h, w);
}

fclose (fr);

The %[^\n]s "eats up" the whole line. I also cannot use %s because the number of words of the names are different. So, I'm wondering if there is anyway to separate the scanning...or is there any better way to approach this problem...

Thank you.

Read the whole line, then find the last two spaces (the ones separating the name from the numbers, and separating the two numbers). Extract the two numbers and parse them, and you're left with the name (probably with some trailing spaces that you can trim). — Some programmer dude, Nov 19 '17 at 13:08

Ed Heal · Accepted Answer · 2017-11-19T13:15:37.243

0

Try

fscanf(fr,"%99[^0-9]%lf%lf ", name, &h, &w)!=EOF)

This will eat the name at the start of the line, then the numbers and then the new line.

You will have to trim the name to remove the spaces at the end. How do I trim leading/trailing whitespace in a standard way? should help you

edited Nov 19 '17 at 13:15

answered Nov 19 '17 at 13:09

Ed Heal

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I should have put `!=EOF` -> `==3` – Ed Heal Nov 19 '17 at 13:23

David C. Rankin · Answer 2 · 2017-11-19T14:36:24.613

Another standard way to approach the problem is simply to use a pointer set to the end of the line, and then backup -- trimming whitespace (and nul-terminating) until a letter or digit is found -- then just backing up until you find then next whitespace. Since your pointer is now pointing to the last whitepace before weight, just save a pointer to current + 1 which will point to the beginning of weight (repeat again for height)

You have now saved a pointer to height and your pointer now points to the last whitespace before height. Just keep backing up over whitespace (nul-terminating as you go) until your either reach the next letter or digit (which will be the end of name) or you hit the beginning of the string (something went wrong and you didn't find `name, height, weight).

Since you have been nul-terminating up to that point, you know the buffer you read now contains only the name, so you can simply print your output and go read the next line. There is absolutely nothing you cannot parse simply by walking a pointer (or pair of pointers) down a string (or up a string in this case)

Putting it altogether, you could do something similar to the following:

#include <stdio.h>
#include <ctype.h>

enum { MAXHW = 2, MAXC = 512 };  /* if you need constants, define them */

int main (int argc, char **argv) {

    char buf[MAXC] = "";    /* line buffer */
    FILE *fp = argc > 1 ? fopen (argv[1], "r") : stdin;

    if (!fp) {  /* validate file open for reading */
        fprintf (stderr, "error: file open failed '%s'.\n", argv[1]);
        return 1;
    }

    while (fgets (buf, MAXC, fp)) { /* read each line */
        char *p = buf,              /* pointer to buf */
             *hw[MAXHW] = {NULL};   /* array of MAXHW pointers */
        int ndx = 0;                /* array index */

        while (*p) p++;             /* find end of buf */
        p--;                        /* backup to last char */

        while (p > buf) {   /* while pointer within buf */
            /* loop checking if char is a trailing space, tab, newline, ... */
            while (p > buf && isspace (*p))
                *p-- = 0;   /* overwrite with nul-terminating char */
            /* loop checking each char is a letter or digit */
            while (p > buf && isalnum (*p))
                p--;        /* just backup to previous char */
            hw[ndx++] = p + 1;  /* space before word found, save ptr to word */
            if (p != buf)   /* if not at beginning */
                *p = 0;     /* nul-terminate */
            else
                break;          /* at beginning - bail */
            if (ndx == MAXHW)   /* if both h & w filled */
                break;          /* bail */
            p--;    /* backup to previous and keep going */
        }
        if (p > buf && ndx == MAXHW) { /* not at beginning & H & W found */
            p--;    /* backup to previous */
            /* trim trailing whitespace to end of name */
            while (p > buf && isspace (*p))
                *p-- = 0;
        }
        /* output results */
        printf ("name: %s, height: %s, weight: %s\n", buf, hw[1], hw[0]);
    }
    if (fp != stdin) fclose (fp);   /* close file if not stdin */

    return 0;
}

Example Use/Output

$ ./bin/readhw <dat/hw.dat
name: Yuri, height: 164, weight: 80
name: Lai San Young, height: 155, weight: 60
name: John Wayne, height: 180, weight: 93

There are many, many different ways you can do this. You could have not used ctype.h and checked, e.g. if (p > buf && (*p == ' ' || *p == '\t' || *p == '\r' || *p == '\n') using the explicit checks for whitespace in lieu of isspace(), etc.. You could have use strpbrk to scan forward in the string for your first digit and worked both forwards and backwards from there. No matter how you do it, the key is to just write your string out on a piece of paper and use a pencil to move your pointer position forward and back while you figure out the testing and indexing you need.

Look things over an let me know if you have further questions.

Separately scanning a sentence and number(s) in C

2 Answers2