read_string_while duplicates character

[George <juergen.sawinski@…>]

Streaming, e.g. "1W" into a multiprecision number will correctly recognize 1, but the first character after the number will be duplicated (from "1W", "WW" is left in the stream).

The cause is the line

is.rdbuf()->sputbackc(static_cast<char>(c));

in read_string_while. The character c does not have to be put back, because snextc first advances position, then returns the character at new position.

[George <juergen.sawinski@…>]

Test

[George <juergen.sawinski@…>]

Provided test file. Result:

$ g++ -o test test.cc -lmpfr
$ ./test
1.0X
1,'XX'
$

Bug is present in 1.62.0, too.

[John Maddock]

Fixed in ​https://github.com/boostorg/multiprecision/commit/1c2ecb6f6ec024d3b7901a50caeab706eda4225f.

Note that I generally need to do a lot more work on the iostream operators.