Parse the jpge file to get the file pixel size

Size limit (lpctstr szfilename) {size sizepiex = {0, 0}; handle hfile = limit; do {hfile = createfile (szfilename, generic_read, file_into_write, null, open_existing, 0, null ); if (hfile = invalid_handle_value) {DWORD dwerr = getlasterror (); _ assert (false) ;}# Pragma pack (push, 1) struct _ tagimgsection_t {byte sectionstart; // It Must Be 0xff byte sectionid; // segment ID: byte sectionlenh, Sectionlenl; // 8-bit long segment // 8-bit low segment length} imgsection; # pragma pack (POP) DWORD dwreaded = 0; // The if ((! Readfile (hfile, & imgsection, 2, & dwreaded, null) | (dwreaded! = 2) | (imgsection. sectionstart! = 0xff) // unlabeled | (imgsection. sectionid! = 0xd8) // non-SOI start header | 0) {_ assert (false); break;} bool bdone = false; while (! Bdone) {memset (& imgsection, 0, sizeof (imgsection); If ((! Readfile (hfile, & imgsection, sizeof (imgsection), & dwreaded, null) | (dwreaded! = Sizeof (imgsection) | 0) break; // If (imgsection. sectionstart! = 0xff) // non-segment mark break; Switch (imgsection. sectionid) {Case (0xff): // The current ID is data {continue;} case (0xd9): // EOI, end of image, end of image {bdone = true; break;} case (0xc0): // sof0, start of frame, frame image start {# pragma pack (push, 1) // one byte of the struct is aligned with the typedef struct _ tagsof0struct_t {struct _ taghead_t {// byte wlenh, wlenl; // ① The data length is 2 bytes ① ~ ⑥ Total length of the six fields byte sample_precision; // ② precision 1 byte the number of digits of each data sample byte highpiexsh, highpiexsl; // ③ Image Height (unit: pixel) byte widthpiexsh, widthpiexsl; // ④ image width (unit: pixels) byte colortabnums; // ⑤ Number of color components} head; // ycrcb is used in jfif, therefore, here the color component quantity is constant 3 struct _ colortab {// 6 color component information color component quantity × 3 bytes (usually 9 bytes) byte Tabid; //) color component Id 1 byte vsampfactor: 4; // low 4 bits: Vertical Sampling factor byte hsampfactory: 4; // high 4 bits: horizontal sampling factor byte curtabid; // ID of the quantified table used by the current component} color Tag [1];} sof0struct; # pragma pack (POP) // restore struct alignment length sof0struct sofodata = {0}; int headlen = sizeof (sofodata. head); If ((! Readfile (hfile, & sofodata, headlen, & dwreaded, null) | dwreaded! = Sizeof (sofodata. head) break; sizepiex. cx = makeword (sofodata. head. widthpiexsl, sofodata. head. widthpiexsh); sizepiex. cy = makeword (sofodata. head. highpiexsl, sofodata. head. highpiexsh); // subsequent omitted ...... Bdone = true; break;} default: {long iSeek = (long) makeword (imgsection. sectionlenl, imgsection. sectionlenh)-2; setfilepointer (hfile, iSeek, null, file_current); break ;}}} while (0); If (hfile! = Invalid_handle_value) {closehandle (hfile);} return sizepiex ;}

// Test cfiledialog filedlg (true); If (filedlg. domodal () = idok) {size imgpiex = getjpgimagepiex (filedlg. getpathname (); cstring szmsg; szmsg. format (_ T ("% s \ n (width = % d Height = % d)"), filedlg. getfilename (), imgpiex. CX, imgpiex. cy); afxmessagebox (szmsg );}