Yalantis/uCrop · error · CImgArgumentException

save_pnk(): Specified filename is (null).

Error message

save_pnk(): Specified filename is (null).

What it means

save_pnk() (Portable Anymap single-channel writer) throws CImgArgumentException when both the FILE* and the filename are null, because there is no output target. It mirrors the same guard used by the other _save_* overloads.

Solutions

1. Pass a non-null filename to save_pnk()
2. Check fopen() return value before passing a FILE*
3. Validate the output path before calling save_pnk()

Example fix

// before
std::FILE *f = std::fopen(path.c_str(), "wb");
img.save_pnk(f); // f may be NULL
// after
std::FILE *f = std::fopen(path.c_str(), "wb");
if (f) img.save_pnk(f); else throw std::runtime_error("cannot open " + path);

if (!file && (!filename || !*filename)) throw std::invalid_argument("save_pnk requires a filename or FILE*");

bool hasDestination(std::FILE *f, const char *name) { return f != NULL || (name != NULL && name[0] != '\0'); }

try { img.save_pnk(path.c_str()); } catch (CImgArgumentException &e) { /* handle */ }

When it happens

Trigger: Calling save_pnk((std::FILE*)0), or _save_pnk with both arguments null; passing a FILE* returned NULL by fopen() without checking.

Common situations: fopen failure not checked before forwarding the stream; null path from environment/config; refactored code that dropped the filename parameter.

Related errors

• save_pfm(): Specified filename is (null).
• save_pnm(): Specified filename is (null).
• save_rgb(): Specified filename is (null).
• save_rgba(): Specified filename is (null).
• load_cimg(): Specified filename is (null).

AI-assisted analysis of Yalantis/uCrop@f788b534b4 (2026-09-08). Data as JSON: /api/errors/65a803a3db205734. Report an issue: GitHub.

Appendix: source

Thrown at ucrop/src/main/jni/CImg.h:62410

      return *this;
    }

    //! Save image as a PNK file.
    /**
      \param filename Filename, as a C-string.
    **/
    const CImg<T>& save_pnk(const char *const filename) const {
      return _save_pnk(0,filename);
    }

    //! Save image as a PNK file \overloading.
    const CImg<T>& save_pnk(std::FILE *const file) const {
      return _save_pnk(file,0);
    }

    const CImg<T>& _save_pnk(std::FILE *const file, const char *const filename) const {
      if (!file && !filename)
        throw CImgArgumentException(_cimg_instance
                                    "save_pnk(): Specified filename is (null).",
                                    cimg_instance);
      if (is_empty()) { cimg::fempty(file,filename); return *this; }
      if (_spectrum>1)
        cimg::warn(_cimg_instance
                   "save_pnk(): Instance is multispectral, only the first channel will be saved in file '%s'.",
                   cimg_instance,
                   filename?filename:"(FILE*)");

      const ulongT buf_size = std::min((ulongT)1024*1024,(ulongT)_width*_height*_depth);
      std::FILE *const nfile = file?file:cimg::fopen(filename,"wb");
      const T *ptr = data(0,0,0,0);

      if (!cimg::type<T>::is_float() && sizeof(T)==1 && _depth<2) // Can be saved as regular PNM file
        _save_pnm(file,filename,0);
      else if (!cimg::type<T>::is_float() && sizeof(T)==1) { // Save as extended P5 file: Binary byte-valued 3D
        std::fprintf(nfile,"P5\n%u %u %u\n255\n",_width,_height,_depth);
        CImg<ucharT> buf((unsigned int)buf_size);

View on GitHub (pinned to f788b534b4)