Function streamStateFromFormat

src/tinyformat.h:680–884

Parse a format string and set the stream state accordingly. The format mini-language recognized here is meant to be the one from C99, with the form "%[flags][width][.precision][length]type" with POSIX positional arguments extension. POSIX positional arguments extension: Conversions can be applied to the nth argument after the format in the argument list, rather than to the next unused argument.

// necessary to pull out variable width and precision.  The function returns a
// pointer to the character after the end of the current format spec.
inline const char* streamStateFromFormat(std::ostream& out, bool& positionalMode,
                                         bool& spacePadPositive,
                                         int& ntrunc, const char* fmtStart,
                                         const detail::FormatArg* args,
                                         int& argIndex, int numArgs)
{
    TINYFORMAT_ASSERT(*fmtStart == '%');
    // Reset stream state to defaults.
    out.width(0);
    out.precision(6);
    out.fill(' ');
    // Reset most flags; ignore irrelevant unitbuf & skipws.
    out.unsetf(std::ios::adjustfield | std::ios::basefield |
               std::ios::floatfield | std::ios::showbase | std::ios::boolalpha |
               std::ios::showpoint | std::ios::showpos | std::ios::uppercase);
    bool precisionSet = false;
    bool widthSet = false;
    int widthExtra = 0;
    const char* c = fmtStart + 1;

    // 1) Parse an argument index (if followed by '$') or a width possibly
    // preceded with '0' flag.
    if (*c >= '0' && *c <= '9') {
        const char tmpc = *c;
        int value = parseIntAndAdvance(c);
        if (*c == '$') {
            // value is an argument index
            if (value > 0 && value <= numArgs)
                argIndex = value - 1;
            else
                TINYFORMAT_ERROR("tinyformat: Positional argument out of range");
            ++c;
            positionalMode = true;
        }
        else if (positionalMode) {
            TINYFORMAT_ERROR("tinyformat: Non-positional argument used after a positional one");
        }
        else {
            if (tmpc == '0') {
                // Use internal padding so that numeric values are
                // formatted correctly, eg -00010 rather than 000-10
                out.fill('0');
                out.setf(std::ios::internal, std::ios::adjustfield);
            }
            if (value != 0) {
                // Nonzero value means that we parsed width.
                widthSet = true;
                out.width(value);
            }
        }
    }
    else if (positionalMode) {
        TINYFORMAT_ERROR("tinyformat: Non-positional argument used after a positional one");
    }
    // 2) Parse flags and width if we did not do it in previous step.
    if (!widthSet) {
        // Parse flags
        for (;; ++c) {