Question

i would like to be able to pass in a format string at runtime and have it applied against a nominal data value.

for example, the incoming format string could look anything like the standard c# format types:

{0:c}, {0:d}, #,###,###

i want to be able to accept the string value and apply the format at runtime. some pseudocode

private string FormatAtRunTime(formatstring)
{
   string formattedOutput = "";
   decimal datavalue = 2.4600;

   datavalue.ToString(formatstring);   ??????

   return formattedOutput;
}

Answer 1

I think you just want:

string formattedOutput = string.Format(formatstring, datavalue);

The fact that the first argument isn’t a string literal (as most calls to Format probably are) is irrelevant.

Note that calling datavalue.ToString(formatstring) would be fine if formatstring were a single format specifier, e.g. “c” or even “0.000” – but it can’t be a composite format string as your example gives. For that, you need string.Format.