bug: wstring_convert to_bytes error

[ivanllc]

Duplicate Check

• I have searched the opened issues and there are no duplicates

Describe the bug

range_error was thrown in -fno-exceptions mode with message "wstring_convert: to_bytes error"
when input in Ubuntu
Answer From Google AI:
https://share.google/aimode/RfMcAz5ELdcenXlTl

Errors during std::wstring_convert::to_bytes typically stem from invalid characters in the input wide string or configuration mismatches with the conversion facet.
Common Causes of Errors

Invalid Encoding: The most frequent cause of a std::range_error is an input string containing [unpaired surrogates](https://stackoverflow.com/questions/32182610/how-can-i-get-wstring-convertto-bytes-to-throw-a-range-error-exception) or characters that exceed the Maxcode limit of the facet.  

Deprecation: std::wstring_convert was [deprecated in C++17](http://en.cppreference.com/w/cpp/locale/wstring_convert.html) due to various usability and safety issues. Modern compilers may issue warnings or require specific flags like -std=c++11 to function.  

Facet Mismatches: If the facet provided to the constructor (e.g., std::codecvt_utf8) does not match the actual encoding of the wide string, the conversion will fail.

Endianness Issues: Using the wrong byte-order (Big-endian vs. Little-endian) can lead to crashes or garbled output during conversion.  

How to Fix or Prevent Crashes

Use Error Initializers: To prevent a std::range_error exception, you can provide a "byte-error string" to the [wstring_convert constructor](https://learn.microsoft.com/en-us/cpp/standard-library/wstring-convert-class?view=msvc-170). If conversion fails, the method returns this string instead of throwing an exception.  

Validate Source Encoding: Ensure your source files and literals are correctly encoded (e.g., using [u8 literals](https://stackoverflow.com/questions/31513578/wstring-converter-exception-when-parsing-a-c-string) like u8"text") to avoid passing invalid bytes to the converter. 

Use Modern Alternatives: Because this class is deprecated, consider using dedicated libraries like ICU (International Components for Unicode) or Boost.Nowide for more robust string handling.

Check Compiler Version: Ensure you are using a compiler with full C++11 support (e.g., GCC 4.9+), as earlier versions had buggy implementations of these facets

Code sample

Code

import flet as ft
from flet import TextField

def main(page: ft.Page):
    new_text = TextField(hint_text="Input some wstring")
    page.add(new_text)

ft.run(main)

To reproduce

When input some Chinese characters in text filed.

Expected behavior

No response

Screenshots / Videos

Captures

Screencast.from.2026-04-04.01-00-50.mp4

Operating System

Linux

Operating system details

Ubuntu 24.04.4 LTS

Flet version

0.82.2

Regression

I'm not sure / I don't know

Suggestions

No response

Logs

Logs

range_error was thrown in -fno-exceptions mode with message "wstring_convert: to_bytes error"

Additional details

Input method IBus Table 1.17.4
Also happen in Android.

[FeodorFitsner]

can you provide an app to reproduce?

[ivanllc]

Screencast.from.2026-04-04.01-00-50.mp4

import flet as ft
from flet import TextField

def main(page: ft.Page):
new_text = TextField(hint_text="Input some wstring")
page.add(new_text)

ft.run(main)

[ivanllc]

I found input some Chinese characters may cause it crash and display this error message in console.
Input method IBus Table 1.17.4
Also happen in Android
Thank you.