Yalantis/uCrop · warning

operator(): Invalid image request, at position [%u].

Error message

operator(): Invalid image request, at position [%u].

What it means

CImgList<T>::operator()(pos) returns the image at index pos in the list. When cimg_verbosity>=3 and pos is out of range (pos>=_width, the list size), it emits a warning and returns a reference to the first image (*_data) instead of crashing. This is a silent-wrong-result hazard: the caller gets image 0 rather than the requested one.

Solutions

1. Check the index against list.size() before calling list(pos)
2. Use cimglist_for or cimglist_forin to iterate instead of manual indices
3. Verify the load actually produced the expected number of frames before accessing them (list.size() check)
4. Enable bounds-checked debugging during development (cimg_verbosity>=3 makes this warn instead of silently returning _data)

Example fix

// before
CImg<unsigned char>& frame = frames(i);
// after
if (i < frames.size()) {
  CImg<unsigned char>& frame = frames(i);
} else {
  // handle missing frame
}

if (i >= 0 && (unsigned)i < frames.size()) { auto& img = frames(i); } else { /* handle */ }

bool inRange(const CImgList<T>& l, unsigned i) { return i < l.size(); }

When it happens

Trigger: Calling list(pos) with an index >= list.size(); iterating a list that was reassigned/emptied (assign()) while old indices are still used; passing a frame index from a failed load (e.g. load_yuv/load_tiff returned fewer frames than requested) into operator().

Common situations: Looping over frames after a partial video/YUV load, reusing stale indices after assign(), off-by-one loops (i<=list.size()), or sharing a CImgList between threads while one thread resizes it.

Related errors

• "[" cimg_appname "_math_parser] CImg<
• "[" cimg_appname "_math_parser] CImg<
• "[" cimg_appname "_math_parser] CImg<
• "[" cimg_appname "_math_parser] CImg<
• data(): Invalid pointer request, at position [%u].

AI-assisted analysis of Yalantis/uCrop@f788b534b4 (2026-09-08). Data as JSON: /api/errors/c98c22e92a771bc8. Report an issue: GitHub.

Appendix: source

Thrown at ucrop/src/main/jni/CImg.h:64691

      static const CImgList<T> _empty;
      return _empty;
    }

    //@}
    //------------------------------------------
    //
    //! \name Overloaded Operators
    //@{
    //------------------------------------------

    //! Return a reference to one image element of the list.
    /**
       \param pos Index of the image element.
    **/
    CImg<T>& operator()(const unsigned int pos) {
#if cimg_verbosity>=3
      if (pos>=_width) {
        cimg::warn(_cimglist_instance
                   "operator(): Invalid image request, at position [%u].",
                   cimglist_instance,
                   pos);
        return *_data;
      }
#endif
      return _data[pos];
    }

    //! Return a reference to one image of the list.
    /**
       \param pos Index of the image element.
    **/
    const CImg<T>& operator()(const unsigned int pos) const {
      return const_cast<CImgList<T>*>(this)->operator()(pos);
    }

    //! Return a reference to one pixel value of one image of the list.

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