Thread: Adding dynamic spaces

Instead of adding spaces, you could use the field width specifier.

Code:

#include <stdio.h>
#include <string.h>

int main(void)
{
    const char *text[] =
    {
        "a string",
        "another string",
        "the longest string",
        "a shorter string",
    };
    size_t i, length [ sizeof(text)/sizeof(*text) ] = {0}, longest = 0;
    /* find the longest string */
    for(i = 0; i < sizeof(text)/sizeof(*text); ++i)
    {
        length[i] = strlen(text[i]);
        if(length[i] > longest)
        {
            longest = length[i];
        }
    }
    /* specify the field width as the length of the longest string */
    printf("%-*s %s\n", (int)longest, "text", "length");
    for(i = 0; i < sizeof(text)/sizeof(*text); ++i)
    {
        printf("%-*s %lu\n", (int)longest, text[i], (unsigned long)length[i]);
    }
    return 0;
}

/* my output
text               length
a string           8
another string     14
the longest string 18
a shorter string   16
*/

>>printf("%-*s %s\n", (int)longest, "text", "length");

For this:
%-*s
The field is a string (%s), the minus sign means left aligned, the * means the length of the field is denoted by the value of the corresponding variable in the subsequent parameters ("longest" in this case). If the length was known at compile time, you would write it like this:
%-10s
for a 10 byte width field.

For this:
(int)longest
the variable longest is of type size_t. In order to conform with the requirements of printf(), it must be cast to an int. This does run the risk of changing the value of the number, as size_t variables can hold a larger number than an int (in general terms), but in this example a high value is unlikely to occur.

Another example to help (maybe!):

Code:

#include <stdio.h>

int main(void) 
{
	const char *myword = "abcd";
	
	printf (">%-20s<\n", myword);
	printf (">%20s<\n", myword);
	printf (">%-*s<\n", 20, myword);
	printf (">%-.2s<\n", myword);
	
	return 0;
}

/*
 Output
 
 >abcd                <
 >                abcd<
 >abcd                <
 >ab<
 
 *
 */