String Padding in C

It might be helpful to know that printf does padding for you, using %-10s as the format string will pad the input right in a field 10 characters long

printf("|%-10s|", "Hello");

will output

|Hello     |

In this case the - symbol means "Left align", the 10 means "Ten characters in field" and the s means you are aligning a string.

Printf style formatting is available in many languages and has plenty of references on the web. Here is one of many pages explaining the formatting flags. As usual WikiPedia's printf page is of help too (mostly a history lesson of how widely printf has spread).

For 'C' there is alternative (more complex) use of [s]printf that does not require any malloc() or pre-formatting, when custom padding is desired.

The trick is to use '*' length specifiers (min and max) for %s, plus a string filled with your padding character to the maximum potential length.

int targetStrLen = 10;           // Target output length  const char *myString="Monkey";   // String for output const char *padding="#####################################################";int padLen = targetStrLen - strlen(myString); // Calc Padding lengthif(padLen < 0) padLen = 0;    // Avoid negative lengthprintf("[%*.*s%s]", padLen, padLen, padding, myString);  // LEFT Padding printf("[%s%*.*s]", myString, padLen, padLen, padding);  // RIGHT Padding 

The "%*.*s" can be placed before OR after your "%s", depending desire for LEFT or RIGHT padding.

[####Monkey] <-- Left padded, "%*.*s%s"
[Monkey####] <-- Right padded, "%s%*.*s"

I found that the PHP printf (here) does support the ability to give a custom padding character, using the single quote (') followed by your custom padding character, within the %s format.
printf("[%'#10s]\n", $s); // use the custom padding character '#'
produces:
[####monkey]

You must make sure that the input string has enough space to hold all the padding characters. Try this:

char hello[11] = "Hello";StringPadRight(hello, 10, "0");

Note that I allocated 11 bytes for the hello string to account for the null terminator at the end.