What causes "load_jpeg(): Specified filename is (null)." in Yalantis/uCrop?

Check the filename/FILE* is non-null before calling load_jpeg

Yalantis/uCrop · error · CImgArgumentException

load_jpeg(): Specified filename is (null).

Error message

load_jpeg(): Specified filename is (null).

What it means

Raised by _load_jpeg()'s validation guard when neither a std::FILE* nor a non-null filename is supplied, so no JPEG source is available ('(null)' is CImg's rendering of the missing filename). The error fires before any libjpeg work starts; provide a valid filename or open file stream to fix it.

Source

Thrown at ucrop/src/main/jni/CImg.h:57014

    struct _cimg_error_mgr {
      struct jpeg_error_mgr original;
      jmp_buf setjmp_buffer;
      char message[JMSG_LENGTH_MAX];
    };

    typedef struct _cimg_error_mgr *_cimg_error_ptr;

    METHODDEF(void) _cimg_jpeg_error_exit(j_common_ptr cinfo) {
      _cimg_error_ptr c_err = (_cimg_error_ptr) cinfo->err; // Return control to the setjmp point
      (*cinfo->err->format_message)(cinfo,c_err->message);
      jpeg_destroy(cinfo); // Clean memory and temp files
      longjmp(c_err->setjmp_buffer,1);
    }
#endif

    CImg<T>& _load_jpeg(std::FILE *const file, const char *const filename) {
      if (!file && !filename)
        throw CImgArgumentException(_cimg_instance
                                    "load_jpeg(): Specified filename is (null).",
                                    cimg_instance);

#ifndef cimg_use_jpeg
      if (file)
        throw CImgIOException(_cimg_instance
                              "load_jpeg(): Unable to load data from '(FILE*)' unless libjpeg is enabled.",
                              cimg_instance);
      else return load_other(filename);
#else

#if defined __GNUC__
      const char *volatile nfilename = filename; // Use 'volatile' to avoid (wrong) g++ warning
      std::FILE *volatile nfile = file?file:cimg::fopen(nfilename,"rb");
#else
      const char *nfilename = filename;
      std::FILE *nfile = file?file:cimg::fopen(nfilename,"rb");
#endif

View on GitHub (pinned to f788b534b4)

Solutions

Check the filename/FILE* is non-null before calling load_jpeg
Check fopen succeeded (and report the errno) before passing the handle
Verify the path string passed across JNI/native boundary is not null
Catch CImgArgumentException to surface the bug during development

Example fix

// before
std::FILE* f = fopen(path,"rb");
img.load_jpeg(f, path); // f may be NULL and path may be NULL
// after
if (!path) throw std::invalid_argument("jpeg path is null");
std::FILE* f = fopen(path,"rb");
if (!f) throw std::runtime_error("cannot open jpeg file");
img.load_jpeg(f, path);

Defensive patterns

Strategy: type-guard

Validate before calling

if (!filename || !*filename) throw std::invalid_argument("filename required");

Type guard

bool hasJpegSource(std::FILE* file, const char* filename) { return file != nullptr || (filename != nullptr && filename[0] != '\0'); }

Try / catch

try { img.load_jpeg(file, filename); }
catch (CImgArgumentException& e) { log("null jpeg source: %s", e.what()); }

Prevention

Always check fopen's return value before use
Validate path strings at API boundaries (JNI GetStringUTFChars null check)
Initialize source variables at declaration
Assert non-null sources in debug builds

When it happens

Trigger: Calling img.load_jpeg(NULL, NULL), or passing a null filename to an overload that expected a FILE* which was never opened.

Common situations: Fopen failed earlier and its null result was passed along un-checked; a JNI string conversion returned null; variable left uninitialized.

Related errors

AI-assisted analysis of Yalantis/uCrop@f788b534b4 (2026-09-08). Data as JSON: /api/errors/1e9a357061f159f8. Report an issue: GitHub.