{"record":{"id":"bca029be0d8f574b","repo":"Yalantis/uCrop","slug":"cimg-fread-only-lu-lu-elements-could-be-read","errorCode":null,"errorMessage":"cimg::fread(): Only %lu/%lu elements could be read from file.","messagePattern":"cimg::fread\\(\\): Only %lu/%lu elements could be read from file\\.","errorType":"console","errorClass":null,"httpStatus":null,"severity":"warning","filePath":"ucrop/src/main/jni/CImg.h","lineNumber":7907,"sourceCode":"       \\return Number of read elements.\n       \\note Same as <tt>std::fread()</tt> but may display warning message if all elements could not be read.\n    **/\n    template<typename T>\n    inline size_t fread(T *const ptr, const size_t nmemb, std::FILE *stream) {\n      if (!ptr || !stream)\n        throw CImgArgumentException(\"cimg::fread(): Invalid reading request of %u %s%s from file %p to buffer %p.\",\n                                    nmemb,cimg::type<T>::string(),nmemb>1?\"s\":\"\",stream,ptr);\n      if (!nmemb) return 0;\n      const size_t wlimitT = 63*1024*1024, wlimit = wlimitT/sizeof(T);\n      size_t to_read = nmemb, al_read = 0, l_to_read = 0, l_al_read = 0;\n      do {\n        l_to_read = (to_read*sizeof(T))<wlimitT?to_read:wlimit;\n        l_al_read = std::fread((void*)(ptr + al_read),sizeof(T),l_to_read,stream);\n        al_read+=l_al_read;\n        to_read-=l_al_read;\n      } while (l_to_read==l_al_read && to_read>0);\n      if (to_read>0)\n        warn(\"cimg::fread(): Only %lu/%lu elements could be read from file.\",\n             (unsigned long)al_read,(unsigned long)nmemb);\n      return al_read;\n    }\n\n    //! Write data to file.\n    /**\n       \\param ptr Pointer to memory buffer containing the binary data to write on file.\n       \\param nmemb Number of elements to write.\n       \\param[out] stream File to write data on.\n       \\return Number of written elements.\n       \\note Similar to <tt>std::fwrite</tt> but may display warning messages if all elements could not be written.\n    **/\n    template<typename T>\n    inline size_t fwrite(const T *ptr, const size_t nmemb, std::FILE *stream) {\n      if (!ptr || !stream)\n        throw CImgArgumentException(\"cimg::fwrite(): Invalid writing request of %u %s%s from buffer %p to file %p.\",\n                                    nmemb,cimg::type<T>::string(),nmemb>1?\"s\":\"\",ptr,stream);\n      if (!nmemb) return 0;","sourceCodeStart":7889,"sourceCodeEnd":7925,"githubUrl":"https://github.com/Yalantis/uCrop/blob/f788b534b48c144edf786c8cddbf0e029e637804/ucrop/src/main/jni/CImg.h#L7889-L7925","documentation":"cimg::fread() reads nmemb elements of size sizeof(T) from a C stream in bounded chunks and emits a non-fatal warning via cimg::warn() when the stream ends (or fails) before all requested elements are read. The return value still gives the number of elements actually read, so the warning signals a short read rather than an exception. CImg image-loading helpers call this when reading pixel data from files.","triggerScenarios":"Calling CImg<T>::fread()/load routines on a file that is smaller than the expected header dimensions declare, a truncated or corrupted binary image, or reading from a FILE* (pipe/network stream) that was closed early.","commonSituations":"Truncated downloads of image files, files corrupted mid-transfer, wrong file passed to a loader expecting a different format/size, network sockets delivered fewer bytes than the image header promised.","solutions":["Check the return value of fread() against the requested element count and abort/re-throw instead of continuing with partial data","Verify the file is complete (re-download/re-copy it) and its size matches what the image header advertises","Validate image width/height/dimensions from the file header against the actual file size before allocating/reading","Wrap the load in error handling that treats a short read as a load failure rather than using the partially filled buffer"],"exampleFix":"// before\nCImg<unsigned char> img;\nimg.load(\"downloaded.png\"); // silently short-reads truncated file\n// after\nstd::FILE* f = std::fopen(\"downloaded.png\", \"rb\");\nstd::fseek(f, 0, SEEK_END); long sz = std::ftell(f); std::fseek(f, 0, SEEK_SET);\nif (sz < (long)expected_min_bytes) throw std::runtime_error(\"file truncated\");\nCImg<unsigned char> img(f);","handlingStrategy":"validation","validationCode":"std::FILE* f = std::fopen(path, \"rb\");\nif (!f) throw std::runtime_error(\"cannot open file\");\nstd::fseek(f, 0, SEEK_END);\nlong sz = std::ftell(f);\nstd::fseek(f, 0, SEEK_SET);\nif (sz < (long)sizeof(T) * expected_nmemb) throw std::runtime_error(\"file too small for image data\");","typeGuard":"bool file_big_enough(std::FILE* f, size_t need_bytes) {\n  long cur = std::ftell(f);\n  std::fseek(f, 0, SEEK_END); long end = std::ftell(f);\n  std::fseek(f, cur, SEEK_SET);\n  return (size_t)(end - cur) >= need_bytes;\n}","tryCatchPattern":null,"preventionTips":["Compare file size against header-declared dimensions before reading pixel data","Never trust partial reads: check fread's return count","Re-transfer files that fail; do not consume truncated images","Prefer loaders that throw on short reads over silent-warn paths"],"tags":["file-io","short-read","truncated-file","cimg"],"backgroundTag":"file-read-failed","analyzedSha":"f788b534b48c144edf786c8cddbf0e029e637804","analyzedAt":"2026-09-08T08:36:04.887Z","contentChangedAt":"2026-09-08T08:36:04.887Z","schemaVersion":2},"datasetVersion":"2026-09-14T05:17:10.506Z"}