jpeg错误打印结构
1 struct jpeg_error_mgr { 2 /* Error exit handler: does not return to caller */ 3 JMETHOD(void, error_exit, (j_common_ptr cinfo)); 4 /* Conditionally emit a trace or warning message */ 5 JMETHOD(void, emit_message, (j_common_ptr cinfo, int msg_level)); 6 /* Routine that actually outputs a trace or error message */ 7 JMETHOD(void, output_message, (j_common_ptr cinfo)); 8 /* Format a message string for the most recent JPEG error or message */ 9 JMETHOD(void, format_message, (j_common_ptr cinfo, char * buffer)); 10 #define JMSG_LENGTH_MAX 200 /* recommended size of format_message buffer */ 11 /* Reset error state variables at start of a new image */ 12 JMETHOD(void, reset_error_mgr, (j_common_ptr cinfo)); 13 14 /* The message ID code and any parameters are saved here. 15 * A message can have one string parameter or up to 8 int parameters. 16 */ 17 int msg_code;//取之参考http://www.cnblogs.com/black-mamba/p/6754493.html 18 #define JMSG_STR_PARM_MAX 80 19 union { 20 int i[8]; 21 char s[JMSG_STR_PARM_MAX]; 22 } msg_parm; 23 24 /* Standard state variables for error facility */ 25 26 int trace_level; /* max msg_level that will be displayed */ 27 28 /* For recoverable corrupt-data errors, we emit a warning message, 29 * but keep going unless emit_message chooses to abort. emit_message 30 * should count warnings in num_warnings. The surrounding application 31 * can check for bad data by seeing if num_warnings is nonzero at the 32 * end of processing. 33 */ 34 long num_warnings; /* number of corrupt-data warnings */ 35 36 /* These fields point to the table(s) of error message strings. 37 * An application can change the table pointer to switch to a different 38 * message list (typically, to change the language in which errors are 39 * reported). Some applications may wish to add additional error codes 40 * that will be handled by the JPEG library error mechanism; the second 41 * table pointer is used for this purpose. 42 * 43 * First table includes all errors generated by JPEG library itself. 44 * Error code 0 is reserved for a "no such error string" message. 45 */ 46 const char * const * jpeg_message_table; /* Library errors */ 47 int last_jpeg_message; /* Table contains strings 0..last_jpeg_message */ 48 /* Second table can be added by application (see cjpeg/djpeg for example). 49 * It contains strings numbered first_addon_message..last_addon_message. 50 */ 51 const char * const * addon_message_table; /* Non-library errors */ 52 int first_addon_message; /* code for first string in addon table */ 53 int last_addon_message; /* code for last string in addon table */ 54 };
jpeg_error_mgr结构体中的函数指针是在调用jpeg_std_error()后被初始化的。可自定义这些函数指针也可使用默认函数。
注意msg_parm支持一个字符串或8个int参数。
jerror.h中包含了一些错误打印宏，下面以ERREXIT1为例进行说明：
1 #define ERREXIT1(cinfo,code,p1) \ 2 ((cinfo)->err->msg_code = (code), \ 3 (cinfo)->err->msg_parm.i[0] = (p1), \ 4 (*(cinfo)->err->error_exit) ((j_common_ptr) (cinfo)))
实际应用中遇到了这么个打印“Improper call to JPEG library in state 202”，那么，这句话是怎么打印出来的呢？
1 cinfo.err = jpeg_std_error(&jerr); 2 cinfo.global_state = 202; 3 (&cinfo)->err->msg_code = (JERR_BAD_STATE); 4 (&cinfo)->err->msg_parm.i[0] = ((&cinfo)->global_state); 5 ((*(&cinfo)->err->error_exit)) ((j_common_ptr) (&cinfo)); 6 7 //ERREXIT1(&cinfo, JERR_BAD_STATE, (&cinfo)->global_state);
line3~5是line7的展开式。第5行中的*间接访问操作符可以不用(http://www.cnblogs.com/black-mamba/p/6765231.html)
<jpegint.h>中包含global_state的值：
/* Values of global_state field (jdapi.c has some dependencies on ordering!) */ #define CSTATE_START 100 /* after create_compress */ #define CSTATE_SCANNING 101 /* start_compress done, write_scanlines OK */ #define CSTATE_RAW_OK 102 /* start_compress done, write_raw_data OK */ #define CSTATE_WRCOEFS 103 /* jpeg_write_coefficients done */ #define DSTATE_START 200 /* after create_decompress */ #define DSTATE_INHEADER 201 /* reading header markers, no SOS yet */ #define DSTATE_READY 202 /* found SOS, ready for start_decompress */ #define DSTATE_PRELOAD 203 /* reading multiscan file in start_decompress*/ #define DSTATE_PRESCAN 204 /* performing dummy pass for 2-pass quant */ #define DSTATE_SCANNING 205 /* start_decompress done, read_scanlines OK */ #define DSTATE_RAW_OK 206 /* start_decompress done, read_raw_data OK */ #define DSTATE_BUFIMAGE 207 /* expecting jpeg_start_output */ #define DSTATE_BUFPOST 208 /* looking for SOS/EOI in jpeg_finish_output */ #define DSTATE_RDCOEFS 209 /* reading file in jpeg_read_coefficients */ #define DSTATE_STOPPING 210 /* looking for EOI in jpeg_finish_decompress */
<jerror.c>
该文件中error_exit()->output_message()->format_message()有如此调用关系。
