I had to do some output formatting in C++ for showing the content of a buffer. Take for instance this buffer:<\/p>\n
\r\nunsigned char buffer [] = \r\n{\r\n 0x00, 0x01, 0x02, 0x03, \r\n 0x04, 0x05, 0x06, 0x07,\r\n 0x08, 0x09, 0x0A, 0x0B,\r\n 0x0C, 0x0D, 0x0E, 0x0F\r\n};\r\n<\/pre>\nI wanted the output to be like this:<\/p>\n
\r\n0x00, 0x01, 0x02, 0x03,\r\n0x04, 0x05, 0x06, 0x07,\r\n0x08, 0x09, 0x0a, 0x0b,\r\n0x0c, 0x0d, 0x0e, 0x0f,\r\n<\/pre>\nThe simples way to do it is like this:<\/p>\n
\r\nfor(int index = 0; index < sizeof(buffer); ++index)\r\n{\r\n std::cout << \"0x\" << std::hex << std::setw(2) << std::setfill('0')\r\n << (int)buffer[index] << std::dec << \", \";\r\n if((index+1) % 4 == 0)\r\n std::cout << std::endl;\r\n}\r\n<\/pre>\nThat for loop achieves the goal. But then, I though, why not using std::copy? Well, the first thing you can come up with is this:<\/p>\n
\r\nstd::copy(\r\n &buffer[0],\r\n &buffer[sizeof(buffer)],\r\n std::ostream_iterator< unsigned char >(std::cout, \" \")\r\n);\r\n<\/pre>\nBut that can only produce this output:<\/p>\n
\r\n ? ? ? ? ? ?\r\n ? ? \r\n<\/pre>\nThat happens because we used unsigned char instead of int for the ostream iterator. You can correct that like this:<\/p>\n
\r\nstd::copy(\r\n &buffer[0],\r\n &buffer[sizeof(buffer)],\r\n std::ostream_iterator< int >(std::cout, \" \")\r\n);\r\n<\/pre>\nand get the output like this:<\/p>\n
\r\n0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15\r\n<\/pre>\nBut this is still far from what I want. The best approach to solve the problem is to use a class that encapsulates a character (or any other type that we want to print), provide a printing function for it and overload the operator<< to output instances of this class. This is shown bellow:<\/p>\n
\r\ntemplate < class T >\r\nclass Printer\r\n{\r\n T value;\r\npublic:\r\n Printer(T val): value(val)\r\n {\r\n }\r\n\r\n void Print(std::ostream& os) const\r\n {\r\n os << \"0x\" << std::hex << std::setw(2) << std::setfill('0')\r\n << (int)value << std::dec << \", \";\r\n }\r\n};\r\n\r\ntemplate < class T >\r\nstd::ostream& operator<<(std::ostream& os, Printer< T > const& elem)\r\n{\r\n elem.Print(os);\r\n return os;\r\n}\r\n<\/pre>\nWe can now transform the copy call to this:<\/p>\n
\r\nstd::copy(\r\n &buffer[0],\r\n &buffer[sizeof(buffer)],\r\n std::ostream_iterator< Printer < unsigned char > >(std::cout)\r\n);\r\n<\/pre>\nand the output is:<\/p>\n
\r\n0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F\r\n<\/pre>\nThat is much better, but not yet perfect. To achieve the final goal, we can transform the Printer class to keep a count of the printer elements:<\/p>\n
\r\ntemplate < class T >\r\nclass Printer\r\n{\r\n static int index;\r\n T value;\r\npublic:\r\n Printer(T val): value(val)\r\n {\r\n }\r\n\r\n void Print(std::ostream& os) const\r\n {\r\n os << \"0x\" << std::hex << std::setw(2) << std::setfill('0')\r\n << (int)value << std::dec << \", \";\r\n if((index+1) % 4 == 0)\r\n os << std::endl;\r\n index++;\r\n }\r\n};\r\ntemplate < class T >\r\nint Printer< T >::index = 0;\r\n\r\ntemplate < class T >\r\nstd::ostream& operator<<(std::ostream& os, Printer< T > const& elem)\r\n{\r\n elem.Print(os);\r\n return os;\r\n}\r\n<\/pre>\nThe copy call remains the same, and the output is:<\/p>\n
\r\n0x00, 0x01, 0x02, 0x03,\r\n0x04, 0x05, 0x06, 0x07,\r\n0x08, 0x09, 0x0a, 0x0b,\r\n0x0c, 0x0d, 0x0e, 0x0f,\r\n<\/pre>\nOf course, if you use this several times, you have to reset the static index from the Printer class. I'll leave that to you.<\/p>\n","protected":false},"excerpt":{"rendered":"
I had to do some output formatting in C++ for showing the content of a buffer. Take for instance this buffer: unsigned char buffer [] = { 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F }; I wanted the output to be like this: 0x00, 0x01, 0x02, … Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_uag_custom_page_level_css":"","advgb_blocks_editor_width":"","advgb_blocks_columns_visual_guide":"","_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[7],"tags":[],"class_list":["post-115","post","type-post","status-publish","format-standard","hentry","category-c"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t