Eric Blake <ebl...@redhat.com> writes: > Pull out a new qstring_append_json_number() helper, so that all > JSON output producers can use a consistent style for printing > floating point without duplicating code (since we are doing more > data massaging than a simple printf format can handle). (For > now, there is only one client, but later patches will use it.) > > Adding a return value will let callers that care diagnose the > situation where an attempt was made to output invalid JSON (which > does not specify Infinity or NaN). None of the current callers > care, but a future patch wants to make it possible to turn this > situation into an error. > > Signed-off-by: Eric Blake <ebl...@redhat.com> [...] > @@ -303,3 +282,39 @@ int qstring_append_json_string(QString *qstring, const > char *str) > qstring_append(qstring, "\""); > return result; > } > + > +/** > + * Append a JSON representation of @number to @qstring. > + * > + * Returns -1 if the added text is not strict JSON, or 0 if the number > + * was finite. > + */
Suggest: * Return 0 if the number is finite, as required by RFC 7159, else -1. The return value makes some sense only for symmetry with qstring_append_json_string(). Without that, I'd ask you to keep this function simple. Callers could just as easily test isfinite() themselves. > +int qstring_append_json_number(QString *qstring, double number) > +{ > + char buffer[1024]; > + int len; > + > + /* FIXME: snprintf() is locale dependent; but JSON requires > + * numbers to be formatted as if in the C locale. Dependence > + * on C locale is a pervasive issue in QEMU. */ > + /* FIXME: This risks printing Inf or NaN, which are not valid > + * JSON values. */ > + /* FIXME: the default precision of 6 for %f often causes > + * rounding errors; we should be using DBL_DECIMAL_DIG (17), > + * and only rounding to a shorter number if the result would > + * still produce the same floating point value. */ > + len = snprintf(buffer, sizeof(buffer), "%f", number); > + assert(len > 0 && len < sizeof(buffer)); > + while (len > 0 && buffer[len - 1] == '0') { > + len--; > + } > + > + if (len && buffer[len - 1] == '.') { > + buffer[len - 1] = 0; > + } else { > + buffer[len] = 0; > + } > + > + qstring_append(qstring, buffer); > + return isfinite(number) ? 0 : -1; > +}