Question

I have string as below,

string str  =  "FX(Y + 1, -(5 * 10) + FML("Test - KB")";

I would like to replace the “-” with “-1 * “. However it should not apply to literal string. For example. FML(“Test – KB”) should NOT be changed to FML(“Test -1 * KB”).

The desired output is “FX(Y + 1, -1 * (5 * 10) + FML(“Test – KB”)”.

Is there a way to do this in regular expression?

Any advice/help is much appreciated.

Answer 1

It will look something like this:

var result = Regex.Replace("FX(Y + 1, -(5 * 10) + FML(\"Test - KB\")",
                           "(?<=^([^\"]|\"[^\"]*\")*)-",
                           "-1 * ");

Regex explanation:

(?<=        # preceded by..
^           # the start of the string, then
([^"]       # either not a " character
|"[^"]*"    # or a string: "..."
)*          # as many times as you want
)
-           # then match the hyphen

Output for your example string is:

FX(Y + 1, -1 * (5 * 10) + FML("Test - KB")

(Note that this doesn’t handle string escapes, if they are supported in your target language.)

This solution will handle strings properly, not just with a heuristic. Here is an example:

FX(Y+1, -(X+Y) + "EMBEDDED: FX(Y + 1, -(5 * 10)" - (X+Y)

Becomes:

FX(Y+1, -1 *(X+Y) + "EMBEDDED: FX(Y + 1, -(5 * 10)" -1 * (X+Y)

Note that the string is not touched even though it “looks like” the other parts.