long doesn't equal another long in C++ -

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it never goes in if statment when 0 == 0 sizeof() of both function return long , regular long both 8, don't know else wrong here.

declarations:

long                        remotestep; // next packet number to-be-processed  long getlong(byte * message, const short offset) {   // long char *     return *(long*)&(message[offset]); }

debug code:

printf("id = %d  remotestep = %d \n", getlong(packet->message, 2), remotestep); printf("id = %d  remotestep = %d \n", getlong(packet->message, 2), remotestep); printf("id = %d  remotestep = %d \n", getlong(packet->message, 2), remotestep); printf("equals = %d \n", getlong(packet->message, 2) == remotestep); printf("sizeof = %d - %d\n", sizeof(getlong(packet->message, 2)), sizeof(remotestep));         // process if expected         if (getlong(packet->message, 2) == remotestep)         {             printf("in.............\n");             ...         }

output information:

id = 0  remotestep = 0 id = 0  remotestep = 0 id = 0  remotestep = 0 equals = 0 sizeof = 8 - 8 id = 1  remotestep = 0 id = 1  remotestep = 0 id = 1  remotestep = 0 equals = 0 sizeof = 8 - 8

i compiled under compat-gcc-34-c++ aka g++34, can't use newer g++ compilers give warnings , errors.

with -wall -wextra

declares.h:1880: warning: int format, different type arg (arg 2) declares.h:1880: warning: int format, different type arg (arg 3) declares.h:1880: warning: unknown conversion type character 0x20 in format declares.h:1880: warning: unknown conversion type character 0x20 in format declares.h:1880: warning: many arguments format declares.h:1881: warning: unknown conversion type character 0x20 in format declares.h:1881: warning: unknown conversion type character 0x20 in format declares.h:1881: warning: many arguments format declares.h:1882: warning: unknown conversion type character 0x20 in format declares.h:1882: warning: unknown conversion type character 0x20 in format declares.h:1882: warning: many arguments format declares.h:1884: warning: int format, different type arg (arg 2) declares.h:1884: warning: int format, different type arg (arg 3)

line 1880 1 of 

printf("id = %l  remotestep = %l \n", getlong(packet->message, 2), remotestep);

the long type should not printed %d, explicitly undefined in specification. example,

each conversion specification introduced '%' character ...
...
if conversion specification not match 1 of above forms, behavior undefined. if argument not correct type corresponding conversion specification, behavior undefined. http://pubs.opengroup.org/onlinepubs/009695399/functions/fprintf.html

(the documentation applies printf fprintf)

thus cannot rely on output of,

printf("id = %d  remotestep = %d \n", getlong(packet->message, 2), remotestep);

to determine that

printf("equals = %d \n", getlong(packet->message, 2) == remotestep); //output: equals = 0

is in fact incorrect, , need fix debug statements first:

printf("id = %ld  remotestep = %ld \n", getlong(packet->message, 2), remotestep);

in case preferable use memcpy instead of pointer cast,

long getlong(byte * message, const short offset) {        long result;     std::memcpy(&result, &(message[offset]), sizeof(long));      return result; }

since long* can have stricter alignment requirement on platform char*.


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