Yalantis/uCrop · error · CImgArgumentException

cimg::fopen(): Specified file path is (null).

Error message

cimg::fopen(): Specified file path is (null).

What it means

cimg::fopen() is CImg's fopen wrapper that throws CImgIOException when a file cannot be opened, instead of returning NULL like std::fopen. Before even attempting the open, it validates its arguments: a null path throws CImgArgumentException with this message. It exists so callers get an explicit, diagnosable error rather than undefined behavior from passing NULL into stdio.

Solutions

1. Check the path for null before calling cimg::fopen, and throw or return a clear error if it is null.
2. If the path comes from getenv, provide a fallback default: const char* p = getenv("X"); if (!p) p = "default.dat";
3. If the path comes from std::string, ensure it is non-empty and pass .c_str() of a live string (watch for dangling c_str() from temporaries).
4. If null is an acceptable runtime condition, catch CImgArgumentException and handle the missing-path case explicitly.

Example fix

// before
std::FILE* f = cimg::fopen(getenv("IMG_PATH"), "r");
// after
const char* path = getenv("IMG_PATH");
if (!path) throw std::runtime_error("IMG_PATH is not set");
std::FILE* f = cimg::fopen(path, "r");

const char* path = getPath();
if (!path || !*path) throw std::runtime_error("file path is missing");
std::FILE* f = cimg::fopen(path, "r");

bool validPath(const char* p) { return p != nullptr && *p != '\0'; }

try {
  std::FILE* f = cimg::fopen(path, "r");
} catch (const CImgArgumentException& e) {
  // path was null: log e.what() and request/derive a valid path
}

When it happens

Trigger: Calling cimg::fopen(0, "r"), or passing a char* path variable that is null — typically a path string that was never assigned, an failed/unchecked path lookup (e.g. getenv returning NULL, a cimg_option/default that is null), or a std::string::c_str() from a moved/empty-managed buffer.

Common situations: getenv("SOME_VAR") returning NULL and being passed straight to fopen; a CImg option or filename argument left unset so the stored const char* is null; loading/saving an image where the filename member was never initialized.

Related errors

• cimg::fempty(): Specified filename is (null).
• cimg::fopen(): File ' ', specified mode is (null).
• cimg::fread(): Invalid reading request of %u
• cimg::fwrite(): Invalid writing request of %u
• cimg::fclose(): Specified file is (null).

AI-assisted analysis of Yalantis/uCrop@f788b534b4 (2026-09-08). Data as JSON: /api/errors/03442d368a5a2fdd. Report an issue: GitHub.

Appendix: source

Thrown at ucrop/src/main/jni/CImg.h:7551

#endif
      }
    }

    // Open a file (similar to std:: fopen(), but with wide character support on Windows).
    inline std::FILE *std_fopen(const char *const path, const char *const mode);


    //! Open a file.
    /**
       \param path Path of the filename to open.
       \param mode C-string describing the opening mode.
       \return Opened file.
       \note Same as <tt>std::fopen()</tt> but throw a \c CImgIOException when
       the specified file cannot be opened, instead of returning \c 0.
    **/
    inline std::FILE *fopen(const char *const path, const char *const mode) {
      if (!path)
        throw CImgArgumentException("cimg::fopen(): Specified file path is (null).");
      if (!mode)
        throw CImgArgumentException("cimg::fopen(): File '%s', specified mode is (null).",
                                    path);
      std::FILE *res = 0;
      if (*path=='-' && (!path[1] || path[1]=='.')) {
        res = (*mode=='r')?cimg::_stdin():cimg::_stdout();
#if cimg_OS==2
        if (*mode && mode[1]=='b') { // Force stdin/stdout to be in binary mode
#ifdef __BORLANDC__
          if (setmode(_fileno(res),0x8000)==-1) res = 0;
#else
          if (_setmode(_fileno(res),0x8000)==-1) res = 0;
#endif
        }
#endif
      } else res = cimg::std_fopen(path,mode);
      if (!res) throw CImgIOException("cimg::fopen(): Failed to open file '%s' with mode '%s'.",
                                      path,mode);

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