Bug 3805 – std.format writeUpToFormatSpec function has subtle loop index bug, will drop character after a %%

private void writeUpToFormatSpec(OutRange, S)(ref OutRange w, ref S fmt) { for (size_t i = 0; i < fmt.length; ++i) { if (fmt[i] != '%') continue; if (fmt[++i] != '%') { // spec found, print and bailout w.put(fmt[0 .. i - 1]); fmt = fmt[i .. $]; return; } // doubled! Now print whatever we had, then update the string // and move on w.put(fmt[0 .. i]); fmt = fmt[i + 1 .. $]; /// BUG !! unable to ever reset a size_t for loop index value to zero, because it is always incremented to 1 at start of next iteration. This means next character after a '%%' will be dropped. i = 0; } /// A better version might look like this. /// Take the i++ out of the for loop top, move it to the first test case. for (size_t i = 0; i < fmt.length;) { if (fmt[i++] != '%') continue; if (fmt[i] != '%') { // spec found, print and bailout w.put(fmt[0 .. i - 1]); fmt = fmt[i .. $]; return; } // doubled! Now print whatever we had, then update the string // and move on w.put(fmt[0 .. i]); fmt = fmt[i + 1 .. $]; i = 0; // OK now, will be 0 at the top of the loop }

Awesome, thank you. It is very subtle indeed.

I think this is same as bug 4775, and it was already fixed. *** This issue has been marked as a duplicate of issue 4775 ***