Having trouble with structs

[C0__0D]

I am reading text from a file and trying to set names to structs. Here is the input file

2
3
Quincy Richard Steven
Donna Elizabeth Francine
5 2 9
4 5 7
5 9 6
4 6 5
7 8 9
6 9 1

Here is the code that I have so far

#include <stdio.h>
#include <stdlib.h>


#define MAX_CHARS 20


// Structure that has 2 properties: name and scores.
struct person
{
    char *name;
    int *scores;
};


int main()
{
    // Opens the file and test to see if the file successfully opens.
    FILE *ifp = fopen("matching.txt", "r");
    if (!ifp)
    {
        printf("Unable to read file!\n");
        return -1;
    }


    // Variables: i is the initializer; num_pairs is the number of pairs; num_events is the number of speed dating events.
    int i, num_pairs, num_events;


    // These two lines read in the number of events and the number of pairs, respectively. TESTED AND READS NUMBER PROPERLY!!!
    fscanf(ifp, "%d", &num_events);
    fscanf(ifp, "%d", &num_pairs);


    // Declares the variable for men, of type struct person.
    struct person *men;
    men = malloc(num_pairs * sizeof(struct person));
    for (i=0; i< num_pairs; i++)
    {
        // This loop creates allocates memory for name and scores for each men.
        men[i].name = malloc(sizeof(char)*MAX_CHARS);
        men[i].scores = malloc(num_pairs * sizeof(int));
    }


    struct person *women;
    women = malloc(num_pairs * sizeof(struct person));
    for (i=0; i< num_pairs; i++)
    {
        // This loop creates allocates memory for name and scores for each women.
        women[i].name = malloc(MAX_CHARS * sizeof(char));
        women[i].scores = malloc(num_pairs * sizeof(int));
    }


    for (i=0; i< num_events; i++)
    {
        int j;
        for (j=0; j< num_pairs; j++)
        {
            fscanf(ifp,"%s", men[j].name);
            printf("%s", men[j].name);


        }


    }


    fclose(ifp);
    return 0;
}

In the nested for-loop it should read in the name of each men and print it out, like so:

Quincy Richard Steven

However it is printing out:

QuincyRichardStevenDonnaElizabethFrancine

Any idea whats going on?

PS. Yes this is homework, but this is one small piece of a much LARGER complex problem, in other words, the answer given here will NOT complete my homework, will just teach a noob something new about structs :-)

[Matticus]

Your problem here isn't with structures, but how you're reading strings.

C string that contains a sequence of characters that control how characters extracted from the stream are treated:

Whitespace character: the function will read and ignore any whitespace characters encountered before the next non-whitespace character (whitespace characters include spaces, newline and tab characters -- see isspace). A single whitespace in the format string validates any quantity of whitespace characters extracted from the stream (including none).

Try replacing it with a function that doesn't care about whitespace (i.e. "fgets()").

[C0__0D]

Try replacing it with a function that doesn't care about whitespace (i.e. "fgets()").

I literally changed this

fscanf(ifp, "%s", men[j].name);

to

fgets(ifp, "%s", men[j].name);

Sorry if this is a dumb mistake, I have NEVER used fgets, ever it wasn't even taught in our intro to C class.

[Matticus]

If you read the link, you'll see that the arguments are in a different order.

1. Where you want to store it (in this case, your struct)
2. How much you want to read (in this case, your #define)
3. From what stream you want to read it (in this case, "ifp")

[C0__0D]

I just changed it to

for (j=0; j< num_pairs; j++)        {
            fgets(men[j].name, MAX_CHARS, ifp);
            printf("%s", men[j].name);
        }

The output is:

Quincy Richard Steven
Donna Elizabeth Francine
5 2 9
4 5 7
5 9 6

men[i].name should have the names of the men and same with the name of the women. Any clue?

[anduril462]

Note, the OP wants to use fscanf. The names are white space separated (mix of space and newline), not strictly newline separated. fgets would read all 3 names into one men[i].name.

The first, little problem is that you simply don't print a space character between names. Just change the printf to "%s " (note the space after %s). That will at least make it a bit more legible.

The second problem is due to you using nested loops. A few helpful printf statements to debug:

    int count = 0;
    for (i=0; i< num_events; i++)
    {
        int j;
        for (j=0; j< num_pairs; j++)
        {
            printf("i = %d, j = %d, loop iterations so far = %d\n", i, j, count);
            fscanf(ifp,"%s", men[j].name);
            printf("%s ", men[j].name);
            printf("scanned into men[%d].name\n", j);
            count++;
        }
    }

And the new output of your program:

i = 0, j = 0, loop iterations so far = 0
Quincy scanned into men[0].name
i = 0, j = 1, loop iterations so far = 1
Richard scanned into men[1].name
i = 0, j = 2, loop iterations so far = 2
Steven scanned into men[2].name
i = 1, j = 0, loop iterations so far = 3
Donna scanned into men[0].name
i = 1, j = 1, loop iterations so far = 4
Elizabeth scanned into men[1].name
i = 1, j = 2, loop iterations so far = 5
Francine scanned into men[2].name

Notice that j repeats going from 0 to 2 twice. The first time it reads the men's names, the second time the women's, which overwrites the men's names. That is a total of 6 iterations, in which you reading and print all of the names. Structure it like your malloc loops, two separate loops, not nested, one for men, one for women.

// no outer loop, one loop for men
for i from 0; < num_pairs
    fscanf into men[i].name
// one loop for women
for i from 0; < num_pairs
    fscanf into women[i].name

[sparkomemphis]

it is printing out QuincyRichardStevenDonnaElizabethFrancine becuase that's what you told it to do.
printf("%s", men[j].name); prints out the string with no added white space ( spaces, tabs , new lines ,etc ).
try printf("%s ",...) to add a space and printf("\n") to add a new line.

 for (i=0; i< num_events; i++)
    {
        int j;
        for (j=0; j< num_pairs; j++)
        {
            fscanf(ifp,"%s", men[j].name);
            printf("%s", men[j].name);
 
 
        }
 
 
    }

[Matticus]

Note, the OP wants to use fscanf.

Yah, noted a bit too late (was working on a correction reply). I was thrown off by the initial proposition, "In the nested for-loop it should read in the name of each men and print it out, like so:"

You're completely right. While not correcting the main problem, I realized that a simple newline in the print statement would make the output more clear for the OP.

My apologies to the OP.

[C0__0D]

Alright solved that little problem, thanks for your guys help! Now I have another little problem...

5 2 9 // QUINCY'S SCORES
4 5 7 // RICHARD'S SCORES
5 9 6 // STEVEN'S SCORES

I am trying to do this, I have been trying to figure out this little problem. I created a generic for-loop:

for (i=0; i< num_pairs; i++
{
    fscanf(ifp, "%d", &men[i].scores);
    printf("%s's scores are %d\n, men[i].name, men[i].scores);

}

For obvious reasons this does not work, but its all I have. Another approach that I was going to take was reading in the whole line as a string and then converting the string into seperate integers. However, I rather avoid this approach. Any hints on solving this problem? I hate asking for all this help, but I really need all the help I can get.

[AndiPersti]

for (i=0; i< num_pairs; i++
{
    fscanf(ifp, "%d", &men[i].scores);
    printf("%s's scores are %d\n, men[i].name, men[i].scores);
}

You want to read three numbers for each man, thus you need two nested for-loops (the outer loop for the men, the inner one for the scores)
men[i].scores is an array, so you are missing the index when you work with one of its elements.

Bye, Andreas