Any function instead of sprintf() in C? code size is too big after compile

Question

I am working on developing an embedded system (Cortex M3). For sending some data from the device to the serial port (to show on a PC screen), I use some own functions using putchar() method.

When I want to send integer or float, I use sprintf() in order to convert them to string of characters and sending them to the serial port.

Now, them problem is that I am using Keil uVision IDE and it is limited version with max 32 KB. Whenever I call sprintf() in different functions, I don't know why the size of the code after compile increased too much. I have surpassed 32 KB now and I wonder I have to change some of my functions and use something else instead of sprintf!

Any clue?

Answer 1

Two potential offerings (neither of which I have used myself - my compiler vendors usually supply a stripped down printf for embedded use):

http://eprintf.sourceforge.net/ - [Sep 2017: unfortunately, seems to have gone away, but source code still here: https://sourceforge.net/projects/eprintf/files/ ]

http://www.sparetimelabs.com/tinyprintf/index.html - 2 files, about 1.4KB code. Option to enable 'longs' (means more code size). Supports leading zeros and field widths. No floating point support.

Answer 2

If you want it to be efficient, the best way is probably to code it yourself, or find some already written code for it on the net. Int to string conversion is however very simple, every programmer can write that in less than 30 minutes. Float to string conversion is a bit more intricate and depends on the floating point format used.

For convenience, here is a simple int-to-string algorithm for use in microcontroller applications:

void get_dec_str (uint8_t* str, size_t len, uint32_t val)
{
  uint8_t i;
  for(i=1; i<=len; i++)
  {
    str[len-i] = (uint8_t) ((val % 10UL) + '0');
    val/=10;
  }

  str[i-1] = '\0';
}