How do I concatenate strings to generate fixed width output

Question

I have an array of structures, where each structure contains a first name and a last name, along with other information. I'm trying to print the array in tabular form, something like this

+---------------------------+--------+--------+
| Student Name              | Test 1 | Test 2 |
+---------------------------+--------+--------+
| Pousseur, Henri           |   95   |   92   |
| Boyer, Charles            |   90   |   97   |
+---------------------------+--------+--------+

However, my output looks like this

+---------------------------+--------+--------+
| Student Name              | Test 1 | Test 2 |
+---------------------------+--------+--------+
| Pousseur, Henri                  |   95   |   92   |
| Boyer, Charles                     |   90   |   97   |
+---------------------------+--------+--------+

My question is, how do I concatenate the last name to the first name (with a comma in between), and then print the whole thing as a fixed width string? So that my table lines up correctly.

Here's my code:

#include <stdio.h>
#define NAME_LEN 25

typedef struct
{
    char fname[NAME_LEN+1];
    char lname[NAME_LEN+1];
    int score1;
    int score2;
} STUREC;

void printRecords(STUREC records[], int count)
{
    printf("+---------------------------+--------+--------+\n");
    printf("| Student Name              | Test 1 | Test 2 |\n");
    printf("+---------------------------+--------+--------+\n");

    for (int i = 0; i < count; i++)
        printf ("| %-s, %-26s| %4d   | %4d   |\n", records[i].lname, records[i].fname, records[i].score1, records[i].score2 );

    printf("+---------------------------+--------+--------+\n");
}

int main(void)
{
    STUREC records[] = {
        { "Henri"  , "Pousseur", 95, 92 },
        { "Charles", "Boyer"   , 90, 97 }
    };

    printRecords(records, 2);
}

Does the code you have posted have any bearing on the question? — user3185968
– user3185968, Commented Apr 20, 2016 at 1:43
Please try to post a minimal example - be specific about the issue you are having and what you have tried, and post the LEAST amount of code needed to reproduce the issue. — nhouser9
– nhouser9, Commented Apr 20, 2016 at 1:44
well i just wanted to show the code... my issue is i can't get the records[count].fname to concatenate onto the end of records[count].lname... i tried using the code i posted in the in the begining, i tried using strcat(s1, s2); — champlooSIXSIX
– champlooSIXSIX, Commented Apr 20, 2016 at 1:47
when i try strcat(records[count].fname, records[count].lname); it compiles, but changes absolutely nothing. — champlooSIXSIX
– champlooSIXSIX, Commented Apr 20, 2016 at 1:50

user3386109 · Accepted Answer · 2016-04-20 02:09:19Z

1

Note that printf returns the number of characters printed. So if you want to print the name within a fixed width, you can print the name, and then output spaces as needed to fill the width.

#define WIDTH 26

int count = printf( "%s, %s", records[i].lname, records[i].fname );
if ( count < WIDTH )
    printf( "%*s", WIDTH-count, "" );

In the format string "%*s", the * tells printf that the width of the string will be passed as an argument. The WIDTH-count argument is the number of spaces that need to be printed, and "" is just an empty string. So for example, if count is 16, then WIDTH-count is 10, so the printf is equivalent to

printf( "%10s", "" );

which will print 10 spaces.

edited Apr 20, 2016 at 2:09

answered Apr 20, 2016 at 1:52

user3386109

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22 Comments

user3386109 Over a year ago

@seanncurtis This code replaces the code that prints the name, where you have printf ("| %-s, %-26s ....

user3386109 Over a year ago

You need to take a step back, and learn how printf works, instead of going off on a tangent with concatenation. For example, printf("hello "); printf("world\n"); does the same thing as printf("hello world\n");

user3386109 Over a year ago

You forgot to remove the records[i].lname.

user3386109 Over a year ago

Ok, I don't really understand that, but if you got it working, great!

champlooSIXSIX Over a year ago

and there it is... perfect. although i wish i understood how to operate the strcat function, this is a nice trick i've learned. thank you very much!

|

sjsam · Accepted Answer · 2016-04-20 02:51:40Z

This is just an adpatation of @user3386109 answer.

Add

#define WIDTH 27 // You get a max width of 26

somewhere in the beginning of your program and a string

char fullname[WIDTH];

somewhere in the beginning of the main.

Then make changes like below :

printf("\n+---------------------------+--------+--------+--------+--------+--------+--------+---------+-------+\n");
    printf("| Student Name              |   ID   | Test 1 | Test 2 | Proj 1 | Proj 2 | Proj 3 | Average | Grade |\n");
    printf("+---------------------------+--------+--------+--------+--------+--------+--------+---------+-------+\n");

    for (i = 0; i < count; i++)
    {
       int lname_len=strlen(records[i].lname);
       int fname_len=strlen(records[i].fname);
        snprintf(fullname,WIDTH,"%s,%s%*s", records[i].lname,records[i].fname,(WIDTH>(lname_len+fname_len)?(WIDTH-(lname_len+fname_len)):0),"");

        /* The above step concatenates - since you're very interested in it -
         * the sirname and the first name into a string fullname making sure
         * that the string is padded to 26 characters utmost.
         */

        printf ("| %s | %-7.6d| %4d   | %4d   | %4d   | %4d   | %4d   | %6.2f  |  %-2s   |\n", fullname, records[i].id, records[i].score1,
                 records[i].score2, records[i].score3, records[i].score4, records[i].score5,
                  records[i].ave, records[i].grade);
    }
    printf("+---------------------------+--------+--------+--------+--------+--------+--------+---------+-------+\n");

    printf("\nHave A Terrible Day!\n\n");

Note the ternary expression :

(WIDTH>(lname_len+fname_len)?(WIDTH-(lname_len+fname_len)):0)

in snprintf. This will be evaluated to unused width, if any which we pad with emptry strings "" or null characters.

If you didn't understand it please have a look here

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