Re: [boost] regex format conditional expression question

How do I use the conditional expression in a format string when my true_expression is a number? For example the format (?1foo) will replace the 1st subexpression with the string foo, but how do I replace the 1st subexpression with 123? I try (?1123) and that fails. I can do (?1 123), but it

[boost] regex format conditional expression question

How do I use the conditional expression in a format string when my true_expression is a number? For example the format (?1foo) will replace the 1st subexpression with the string foo, but how do I replace the 1st subexpression with 123? I try (?1123) and that fails. I can do (?1 123), but it gives