cost of fprintf

Question

I am developing an embedded application in C++ for a platform with limited code/data RAM, but rather unlimited RAM for filesystem usage.

While looking for reducing t

Answer 1

In embedded systems, printf can sometimes drag in all the floating point support for format strings like %f.

More intelligent environments will make the floating point options for printf an optional thing.

But even for integers, there's a lot of general purpose code in printf and you may find it's more compact to write your own routines, tailored to your specific needs, like:

outInt (char *buff, int intVal);
outChr (char *buff, char chVal);
outStr (char *buff, char *strVal);

and so on, for writing to buffers, then outBuff (char *buff) for sending it to a file or standard output.

---

For example, if you control the data being used (no string overflow, 16-bit twos complement integers and such), you can use the following functions:

#include 
#include 
#include 

void outChr (char *buff, char chVal) {
    *buff++ = chVal;
    *buff = '\0';
}

void outStr (char *buff, char *strVal) {
    strcpy (buff, strVal);
}

 

void outInt (char *buff, int intVal) {
    int divisor = 10000, printing = 0;

    // Special cases.

    if (intVal == -32768) { outStr (buff, "-32768"); return; }
    if (intVal ==      0) { outChr (buff,      '0'); return; }

    // Handle negatives.

    if (intVal < 0) { outChr (buff++, '-'); intVal = -intVal; }

    // Handle non-zero positives <= 32767.

    while (divisor > 0) {
        if ((intVal >= divisor) || printing) {
            outChr (buff++, "0123456789"[intVal/divisor]);
            printing = 1;
        }
        intVal = intVal % divisor;
        divisor /= 10;
    }
}

 

int main (int argc, char *argv[]) {
    char buff[1000];
    int i;
    for (i = 1; i < argc; i++) {
        outInt (buff, atoi (argv[i]));
        printf ("[%s] -> [%s]\n", argv[i], buff);
    }
    return 0;
}

Running this with:

pax$ tstprg 32767 10000 9999 10 9 1 0 -1 -9 -10 -99 -10000 -32767 -32768

outputs:

[32767] -> [32767]
[10000] -> [10000]
[9999] -> [9999]
[10] -> [10]
[9] -> [9]
[1] -> [1]
[0] -> [0]
[-1] -> [-1]
[-9] -> [-9]
[-10] -> [-10]
[-99] -> [-99]
[-10000] -> [-10000]
[-32767] -> [-32767]
[-32768] -> [-32768]

These functions should be relatively small in size since they're targeted to specific needs rather than the far more general printf family.