![\"temple](\"https:\/\/www.modernescpp.com\/wp-content\/uploads\/2019\/06\/temple-1717088_1280.jpg\")
<\/p>\n
Input and Output Functions<\/h2>\n
C++ has four predefined stream objects for the convenience of dealing with the keyboard and the monitor.<\/p>\n
![\"PredefinedStreamObject\"](\"https:\/\/www.modernescpp.com\/wp-content\/uploads\/2019\/06\/PredefinedStreamObject.png\")
<\/p>\n
The stream objects can be used to write a program that reads from the command line and returns the sum.<\/p>\n
\/\/<\/span> Iostreams.<\/span>cpp\r\n\r\n#include <iostream><\/span>\r\n\r\nint<\/span> main(){\r\n\r\n std::cout <<<\/span> std::endl;\r\n \r\n std::cout <<<\/span> \"Type in your numbers(Quit with an arbitrary character): \"<\/span> <<<\/span> std::endl;\r\n \r\n int<\/span> sum<\/span>{0<\/span>};\r\n int<\/span> val;\r\n\r\n while<\/span> ( std::cin >><\/span> val ) sum<\/span> +=<\/span> val;\r\n\r\n std::cout <<<\/span> \"Sum: \"<\/span> <<<\/span> sum<\/span> <<<\/span> std::endl;\r\n \r\n std::cout <<<\/span> std::endl;\r\n\r\n}\r\n<\/pre>\n<\/div>\n <\/p>\n
![\"Iostreams\"](\"https:\/\/www.modernescpp.com\/wp-content\/uploads\/2019\/06\/Iostreams.png\")
<\/p>\n
The program uses the stream operators <<<\/span> and >><\/span> and the stream manipulator std::endl<\/span>.<\/p>\n\n- The insert operator <<<\/span> pushes characters onto the output stream std::cout<\/span>.<\/li>\n
- The extract operator >><\/span> pulls the characters from the input stream std::cin. <\/span><\/li>\n
- You can build chains of insert or extract operators because both operators return a reference to themselves.<\/li>\n<\/ul>\n
std::endl<\/span> is a stream manipulator because it puts a \u2018\\n\u2019<\/span> character onto std::cout<\/span> and flushes the output buffer.<\/p>\nHere are the most frequently used stream manipulators.<\/p>\n
![\"StreamManipulators\"](\"https:\/\/www.modernescpp.com\/wp-content\/uploads\/2019\/06\/StreamManipulators.png\")
Input<\/h3>\n
You can read in two ways from the input stream: Formatted with the extractor >><\/span> and unformatted with explicit methods.<\/p>\n<\/p>\nFormatted Input<\/h4>\n
The extract operator >><\/span><\/p>\n\n- is predefined for all built-in types and strings,<\/li>\n
- can be implemented for user-defined data types,<\/li>\n
- can be configured by format specifiers.<\/li>\n<\/ul>\n
The following code snippet shows a straightforward way to read two int<\/span>‘s.<\/p>\n\n#include <iostream><\/span>\r\n...<\/span>\r\nint<\/span> a, b;\r\nstd::cout <<<\/span> \"Two natural numbers: \"<\/span> <<<\/span> std::endl;\r\nstd::cin >><\/span> a >><\/span> b; \/\/<\/span> <<\/span> 2000<\/span> 11<\/span>><\/span>\r\nstd::cout <<<\/span> \"a: \"<\/span> <<<\/span> a <<<\/span> \" b: \"<\/span> <<<\/span> b;\r\n<\/pre>\n<\/div>\n <\/p>\n
std::cin<\/span> ignores by default leading whitespace.<\/p>\nUnformatted Input<\/h4>\n
An input stream supports a few methods for unformatted input.<\/p>\n
![\"UnformattedInput\"](\"https:\/\/www.modernescpp.com\/wp-content\/uploads\/2019\/06\/UnformattedInput.png\")
<\/p>\n
\n- std::string<\/span> has a getline<\/span> function<\/strong><\/li>\n<\/ul>\n
The getline<\/span> <\/a>function of std::string<\/span> has a big advantage over the getline<\/span> function of the istream.<\/span> The std::string<\/span> automatically takes care of its memory. On the contrary, you have to reserve the memory for the buffer buf<\/span> in the call is.get(buf, num)<\/span>. Using the getline<\/span> function is quite convenient because you can also specify a delimiter:<\/p>\n <\/p>\n
\n\/\/<\/span> inputUnformatted.<\/span>cpp\r\n\r\n#include <fstream><\/span>\r\n#include <iostream><\/span>\r\n#include <string><\/span>\r\n\r\nint<\/span> main(){\r\n\r\n std::cout <<<\/span> std::endl;\r\n\r\n std::string line;\r\n std::cout <<<\/span> \"Write a line: \"<\/span> <<<\/span> std::endl;\r\n std::getline(std::cin, line); \/\/<\/span> (1<\/span>)\r\n std::cout <<<\/span> line <<<\/span> std::endl;\r\n\r\n std::cout <<<\/span> std::endl;\r\n \r\n std::ifstream inputFile(\"test.txt\"<\/span>); \r\n while<\/span> ( std::getline(inputFile, line, ';'<\/span>) ) { \/\/<\/span> (2<\/span>)\r\n std::cout <<<\/span> line <<<\/span> std::endl;\r\n }\r\n\r\n}\r\n<\/pre>\n<\/div>\n <\/p>\n
First, the program reads in line (1) for std::cin<\/span>; second, it reads in line (2) from the file test.txt<\/span>.<\/p>\nFor simplicity reasons, the code does no error handling. You can read the error handling details in my last post: C++ Core Guidelines: iostreams.<\/a> The file test.txt<\/span> contains numbers, which are separated by “;”<\/span>. <\/p>\n ![\"inputUnformatted\"](\"https:\/\/www.modernescpp.com\/wp-content\/uploads\/2019\/06\/inputUnformatted.png\")
<\/p>\n
Output<\/h3>\n
![\"formatSpecifier\"](\"https:\/\/www.modernescpp.com\/wp-content\/uploads\/2019\/06\/formatSpecifier.png\")
<\/p>\n![\"BooleanValue\"](\"https:\/\/www.modernescpp.com\/wp-content\/uploads\/2019\/06\/BooleanValue.png\")
<\/p>\n![\"FieldWithAndFillCharacters\"](\"https:\/\/www.modernescpp.com\/wp-content\/uploads\/2019\/06\/FieldWithAndFillCharacters.png\")
<\/p>\n![\"Alignment\"](\"https:\/\/www.modernescpp.com\/wp-content\/uploads\/2019\/06\/Alignment.png\")
<\/h4>\n![\"FloatingPointNumbers\"](\"https:\/\/www.modernescpp.com\/wp-content\/uploads\/2019\/06\/FloatingPointNumbers.png\")
<\/p>\n![\"NumericBase\"](\"https:\/\/www.modernescpp.com\/wp-content\/uploads\/2019\/06\/NumericBase.png\")
<\/p>\n