uCalc API Version: 2.1.3-preview.2 Released: 6/17/2026

Warning

uCalc API Preview Release Notice:The documentation describes the intended behavior of the API. The current preview build contains incomplete features, unoptimized performance, and is subject to breaking changes.

ReturnStr

Method

Product: 

Fast Math Parser

Class: 

Callback

Sets the string return value for a user-defined callback function, passing it back to the uCalc expression engine.

Syntax

ReturnStr(string)

Parameters

returnValue
string
The string value that the callback function should return to the expression evaluator.

Return

void

This method does not return a value to the host application; it communicates the return value back to the uCalc engine via the callback object.

Remarks

The ReturnStr method is the mechanism for sending a string result from a native callback function back to the uCalc evaluation engine. When a custom function defined with As String is called within an expression, this method must be used to provide its output.

⚙️ Type-Specific Returns

This method is specifically for returning string values. uCalc provides a family of type-safe return methods for other data types. Using the correct method ensures data integrity and avoids unnecessary type conversions.

💡 Comparative Analysis

Unlike a native return statement in C# or C++, which is a language-level control flow keyword, cb.ReturnStr() is a method call that interacts with the uCalc engine's internal state. It effectively places the provided value onto the evaluation stack, allowing the engine to continue processing the expression. This distinction is crucial: the callback function itself is typically void in the host language, and cb.ReturnStr() is the designated channel for communicating results back to the parser.

Examples

Returning a string (from a callback)
				
					using uCalcSoftware;

var uc = new uCalc();

static void TwiceStr(uCalc.Callback cb) {
   cb.ReturnStr(cb.ArgStr(1) + cb.ArgStr(1));
}

uc.DefineFunction("Twice(Txt As String) As String", TwiceStr);
Console.WriteLine(uc.EvalStr("Twice('Bye')"));
				
			
ByeBye
				
					#include <iostream>
#include "uCalc.h"

using namespace std;
using namespace uCalcSoftware;

void ucalc_call TwiceStr(uCalcBase::Callback cb) {
   cb.ReturnStr(cb.ArgStr(1) + cb.ArgStr(1));
}
int main() {
   uCalc uc;
   uc.DefineFunction("Twice(Txt As String) As String", TwiceStr);
   cout << uc.EvalStr("Twice('Bye')") << endl;
}
				
			
ByeBye
				
					Imports System
Imports uCalcSoftware
Public Module Program
   
   Public Sub TwiceStr(ByVal cb As uCalc.Callback)
      cb.ReturnStr(cb.ArgStr(1) + cb.ArgStr(1))
   End Sub
   Public Sub Main()
      Dim uc As New uCalc()
      uc.DefineFunction("Twice(Txt As String) As String", AddressOf TwiceStr)
      Console.WriteLine(uc.EvalStr("Twice('Bye')"))
   End Sub
End Module
				
			
ByeBye
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