padding with sprintf

Question

I have a dummy question. I would like to print an integer into a buffer padding with 0 but I cannot sort it out the sprintfformat. I am trying the following

char buf[31];
int my_val = 324;
sprintf( buf, "%d030", my_val );

hoping to have the following string

"000000000000000000000000000324"

what am I doing wrong? It doesn't mean pad with 0 for a max width of 30 chars?

Solution 1

"%030d" is the droid you are looking for

Solution 2

You got the syntax slightly wrong; The following code produces the desired output:

char buf[31];
int my_val = 324;
sprintf( buf, "%030d", (int)my_val );

From Wikipedia's Article on Printf:

[...] printf("%2d", 3) results in " 3", while printf("%02d", 3) results in "03".

Solution 3

The padding and width come before the type specifier:

sprintf( buf, "%030d", my_val );

Solution 4

Try:

sprintf( buf, "%030d", my_val );

Solution 5

Your precision and width parameters need to go between the '%' and the conversion specifier 'd', not after. In fact all flags do. So if you want a preceeding '+' for positive numbers, use '%+d'.

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Comments

[Matthew]

You probably already know this, but using snprintf style functions where you specify the buffer length is a good habit to get yourself in, as it helps prevent buffer overflows.

[kevinji]

Why do you need to cast my_val to int when it's already an int?

[Jens]

"The droids you are looking for are in the manual. They are called width and precision." :-)