C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  print a byte number with cout          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message Mastupristi Guest Posted: Thu Feb 24, 2005 4:01 pm    Post subject: print a byte number with cout I have an array of char for example: char tag[] = {1, 'W', 0xFF, 0xFF}; I want to obtain: 01 57 FF FF if I try with: #include <iostream> #include <iomanip> using namespace std; static const char tag[] = {1, 'W', 0xFF, 0xFF}; int main(void) { ios::fmtflags old = cout.flags(); for(int i = 0; i< 4; i++) cout << hex << uppercase << setw(2) << setfill('0') << (unsigned char)tag[i] << " "; cout.flags(old); cout< return 0; } I obtain: 0 0W 0ÿ 0ÿ If I modify the cast from (unsigned char)tag[i] to (unsigned short)tag[i] I obtain: 01 57 FFFF FFFF I don't want to use printf, but with it could be simpler: #include static const char tag[] = {1, 'W', 0xFF, 0xFF}; int main(void) { for(int i = 0; i< 4; i++) printf("%02hhX ",tag[i]); printf("n"); return 0; } so, how to print a byte numbe in hex format using cout? thanks -- Mastupristi? Back to top Johan Guest Posted: Thu Feb 24, 2005 4:14 pm    Post subject: Re: print a byte number with cout HI, First you have to cast tag[i] to int; for example int val = tag[i]; cout << hex << setw(2) << setfill('0') << val << endl; regards Johan "Mastupristi" news:20050224170131.000001f9.cialdi_NO_SP (AT) AM_gmail (DOT) com... I have an array of char for example: char tag[] = {1, 'W', 0xFF, 0xFF}; I want to obtain: 01 57 FF FF if I try with: #include <iostream> #include <iomanip> using namespace std; static const char tag[] = {1, 'W', 0xFF, 0xFF}; int main(void) { ios::fmtflags old = cout.flags(); for(int i = 0; i< 4; i++) cout << hex << uppercase << setw(2) << setfill('0') << (unsigned char)tag[i] << " "; cout.flags(old); cout< return 0; } I obtain: 0 0W 0ÿ 0ÿ If I modify the cast from (unsigned char)tag[i] to (unsigned short)tag[i] I obtain: 01 57 FFFF FFFF I don't want to use printf, but with it could be simpler: #include static const char tag[] = {1, 'W', 0xFF, 0xFF}; int main(void) { for(int i = 0; i< 4; i++) printf("%02hhX ",tag[i]); printf("n"); return 0; } so, how to print a byte numbe in hex format using cout? thanks -- Mastupristi? Back to top Dietmar Kuehl Guest Posted: Thu Feb 24, 2005 5:52 pm    Post subject: Re: print a byte number with cout Johan wrote: Quote: First you have to cast tag[i] to int; For signed chars with negative values this actually does the wrong thing: the sign is extended to fit the bigger integer type which results in a value with all the higher bits being set. What the original author has to do is to first cast the signed character to an unsigned character and then to an appropriate integer type: when casting to the unsigned character type, the bits remain unchanged and for unsigned types there is no sign extension - obviously, since they don't have a sign. That is, the code would look something like this: std::cout << int(static_cast assuming the stream is setup appropriately to fit the desired formatting. BTW, note that you need to go through a similar procedure if you want to use C's character classification function like 'isspace()': these are only defined for unsigned character values but often the type 'char' is signed (the standard makes not guarantee about the signedness of 'char'). -- <mailto:dietmar_kuehl (AT) yahoo (DOT) com> <http://www.dietmar-kuehl.de/> <http://www.contendix.com> - Software Development & Consulting Back to top Old Wolf Guest Posted: Thu Feb 24, 2005 10:58 pm    Post subject: Re: print a byte number with cout Mastupristi wrote: Quote: I have an array of char for example: char tag[] = {1, 'W', 0xFF, 0xFF}; I want to obtain: 01 57 FF FF if I try with: #include #include using namespace std; static const char tag[] = {1, 'W', 0xFF, 0xFF}; Change this to unsigned char. 0xFF is not a valid char on your system. Quote: int main(void) { ios::fmtflags old = cout.flags(); for(int i = 0; i< 4; i++) cout << hex << uppercase << setw(2) setfill('0') (unsigned char)tag[i] << " "; Change that to int(tag[i]) Quote: I obtain: 0 0W 0ÿ 0ÿ If I modify the cast from (unsigned char)tag[i] to (unsigned short)tag[i] I obtain: 01 57 FFFF FFFF Back to top Raymond Martineau Guest Posted: Thu Feb 24, 2005 11:00 pm    Post subject: Re: print a byte number with cout On Thu, 24 Feb 2005 17:01:31 +0100, Mastupristi <cialdi_NO_SP (AT) AM_gmail (DOT) com> wrote: [...] Quote: static const char tag[] = {1, 'W', 0xFF, 0xFF}; int main(void) { ios::fmtflags old = cout.flags(); for(int i = 0; i< 4; i++) cout << hex << uppercase << setw(2) setfill('0') (unsigned char)tag[i] << " "; [...] If I modify the cast from (unsigned char)tag[i] to (unsigned short)tag[i] I obtain: 01 57 FFFF FFFF This casts a signed char to an unsigned short, which results in the undesired behaviour. The easiest way to fix this is to change tag[] to an unsigned char array, but this may cause side-effects. Another poster suggested a better method - cast to unsigned char, and cast the result to an integer or short. Quote: I don't want to use printf, but with it could be simpler: #include It's best to use global mainspace free from clutter. 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