若定义JMESSAGE(code,string)code ,宏，就表示enum list of message codes.
若定义JMESSAGE(code,string)string ,宏，就可表示a message string table.
==========================================================================
<jerror.h>
1 #ifndef JMESSAGE 2 #ifndef JERROR_H 3 /* First time through, define the enum list */ 4 #define JMAKE_ENUM_LIST 5 #else 6 /* Repeated inclusions of this file are no-ops unless JMESSAGE is defined */ 7 #define JMESSAGE(code,string) 8 #endif /* JERROR_H */ 9 #endif /* JMESSAGE */ 10 11 #ifdef JMAKE_ENUM_LIST 12 13 typedef enum { 14 15 #define JMESSAGE(code,string) code , 16 17 #endif /* JMAKE_ENUM_LIST */ 18 19 JMESSAGE(JMSG_NOMESSAGE, "Bogus message code %d") /* Must be first entry! */ 20 21 /* For maintenance convenience, list is alphabetical by message code name */ 22 JMESSAGE(JERR_BAD_ALIGN_TYPE, "ALIGN_TYPE is wrong, please fix") 23 JMESSAGE(JERR_BAD_ALLOC_CHUNK, "MAX_ALLOC_CHUNK is wrong, please fix") 24 ...... 25 ...... 26 ...... 27 JMESSAGE(JWRN_NOT_SEQUENTIAL, "Invalid SOS parameters for sequential JPEG") 28 JMESSAGE(JWRN_TOO_MUCH_DATA, "Application transferred too many scanlines") 29 30 #ifdef JMAKE_ENUM_LIST 31 32 JMSG_LASTMSGCODE 33 } J_MESSAGE_CODE; 34 35 #undef JMAKE_ENUM_LIST 36 #endif /* JMAKE_ENUM_LIST */ 37 38 /* Zap JMESSAGE macro so that future re-inclusions do nothing by default */ 39 #undef JMESSAGE
那么,在.c文件中怎样使用message codes和对应的message desription string呢?
1 #include “jerror.h”//这一次是为了定义enum list of message codes 2 #define JMESSAGE(code,string) string , 3 4 const char * const jpeg_std_message_table[] = { 5 #include "jerror.h"//这一次是为了定义message string table 6 NULL 7 };
上述的代码复用率就非常高。
预编译后的形式如下：
1 # 1 "main.c" 2 # 1 "<built-in>" 3 # 1 "<command-line>" 4 # 1 "/usr/include/stdc-predef.h" 1 3 4 5 # 1 "<command-line>" 2 6 # 1 "main.c" 7 8 # 1 "jerror.h" 1 9 # 19 "jerror.h" 10 typedef enum { 11 12 JMSG_NOMESSAGE , 13 14 15 JERR_ARITH_NOTIMPL , 16 17 JERR_BAD_ALIGN_TYPE , 18 JERR_BAD_ALLOC_CHUNK , 19 JWRN_JPEG_EOF , 20 JWRN_MUST_RESYNC , 21 22 JWRN_NOT_SEQUENTIAL , 23 JWRN_TOO_MUCH_DATA , 24 25 26 27 JMSG_LASTMSGCODE 28 } J_MESSAGE_CODE; 29 # 3 "main.c" 2 30 31 32 33 const char * const jpeg_std_message_table[] = { 34 # 1 "jerror.h" 1 35 # 25 "jerror.h" 36 "Bogus message code %d" , 37 38 39 "Sorry, there are legal restrictions on arithmetic coding" , 40 41 "ALIGN_TYPE is wrong, please fix" , 42 "MAX_ALLOC_CHUNK is wrong, please fix" , 43 "Premature end of JPEG file" , 44 "Corrupt JPEG data: found marker 0x%02x instead of RST%d" , 45 46 "Invalid SOS parameters for sequential JPEG" , 47 "Application transferred too many scanlines" , 48 # 8 "main.c" 2 49 NULL 50 }; 51 52 int main(int argc, char** argv) 53 { 54 55 printf("%s ", jpeg_std_message_table[JERR_ARITH_NOTIMPL]); 56 57 return 0; 58 }
若定义JMESSAGE(code,string)code ,宏，就表示enum list of message codes.
若定义JMESSAGE(code,string)string ,宏，就可表示a message string table.