engfmt

Here is a simple library for converting ASCII floating point numbers (perhaps the result from sprintf) into "engineering format"- so that the exponent is a multiple of 3.

Also included is a function to insert commas between every three digits.

Interface

extern char *engfmt(char *d, size_t d_len, const char *s);

's' is pointer to a zero-terimnated ASCII floating point number.

'd'/'d_len' contains pointer and size of a buffer for the result.

Returns 'd'.

extern char *insert_commas(char *dst, const char *src, char sep);

'src' is pointer to zero-terminated ASCII decimal or floating
pointer number.

'dst' is pointer to a buffer.

'sep' is separator character to insert, typically ',' or '_'.

Returns 'dst'.

Try it

Here is a simple demo main.c:

    char buf[80];
    char buf1[80];
    printf("%s\n", engfmt(buf, sizeof(buf), argv[1]));
    printf("%s\n", insert_commas(buf1, buf, ','));

Here is the result:

laptop:~/engfmt$ make
cc    -c -o engfmt.o engfmt.c
cc    -c -o main.o main.c
cc -o engfmt engfmt.o main.o

    laptop:~/$ ./engfmt 1.2345
    1.2345
    1.234,5
    laptop:~/engfmt$ ./engfmt 1.2345e0
    1.2345
    1.234,5
    laptop:~/engfmt$ ./engfmt 1.2345e1
    12.345
    12.345
    laptop:~/engfmt$ ./engfmt 1.2345e2
    123.45
    123.45
    laptop:~/engfmt$ ./engfmt 1.2345e3
    1.2345e3
    1.234,5e3
    laptop:~/engfmt$ ./engfmt 1.2345e4
    12.345e3
    12.345e3
    laptop:~/engfmt$ ./engfmt 1.2345e5
    123.45e3
    123.45e3
    laptop:~/engfmt$ ./engfmt 1.2345e6
    1.2345e6
    1.234,5e6
    laptop:~/engfmt$ ./engfmt 1.2345e7
    12.345e6
    12.345e6
    laptop:~/engfmt$ ./engfmt 1.2345e-1
    123.45e-3
    123.45e-3
    laptop:~/engfmt$ ./engfmt 1.2345e-2
    12.345e-3
    12.345e-3
    laptop:~/engfmt$ ./engfmt 1.2345e-3
    1.2345e-3
    1.234,5e-3
    laptop:~/engfmt$ ./engfmt 1.2345e-4
    123.45e-6
    123.45e-6
    laptop:~/engfmt$ ./engfmt 1.2345e-5
    12.345e-6
    12.345e-6
    laptop:~/engfmt$ ./engfmt 1.2345e-6
    1.2345e-6
    1.234,5e-6
    laptop:~/engfmt$ ./engfmt 1.2345e-7
    123.45e-9
    123.45e-9