{"id":1863,"date":"2025-01-25T20:42:33","date_gmt":"2025-01-25T20:42:33","guid":{"rendered":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/?page_id=1863"},"modified":"2025-01-25T21:45:11","modified_gmt":"2025-01-25T21:45:11","slug":"input-of-user-defined-types","status":"publish","type":"page","link":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/topics\/c-details\/i-o-streams\/input-of-user-defined-types\/","title":{"rendered":"Input of User-Defined Types"},"content":{"rendered":"\n

<\/span>Input of User-Defined Types<\/span><\/h2>\n\n\n\n

Input may be defined in a similar way:<\/p>\n\n\n\n

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<\/path><\/path><\/svg><\/span>
class<\/span> <\/span>Person<\/span><\/span>\n{<\/span><\/span>\npublic:<\/span><\/span>\n\t\/\/ \u2026<\/span><\/span>\n\t<\/span>friend<\/span><\/span>\n\t<\/span>istream<\/span> <\/span>&<\/span>operator>><\/span>(<\/span>istream<\/span> <\/span>&<\/span>os<\/span>, <\/span>Person<\/span> <\/span>&<\/span>p<\/span>);<\/span><\/span>\nprivate:<\/span><\/span>\n\t\/\/ \u2026<\/span><\/span>\n};<\/span><\/span><\/code><\/pre><\/div>\n<\/div>\n\n\n\n
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But it’s a little trickier on input, because you have to get the formatting exactly right (just as scanf()<\/strong> is trickier to use than printf() <\/strong>in C).<\/p>\n<\/div>\n<\/div>\n\n\n\n
<\/span>Example<\/span><\/h3>\n\n\n\n
Let’s assume that we wish to read back the exact same stuff we output before from the cout << p<\/code><\/strong>, including labels:<\/p>\n\n\n\n
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<\/path><\/path><\/svg><\/span>
\/\/<\/span><\/span>\n\/\/  Person.h<\/span><\/span>\n\/\/  iostreams - User-defined types<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 9\/4\/24.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#ifndef<\/span> Person_h<\/span><\/span>\n#define<\/span> Person_h<\/span><\/span>\n<\/span>\n#include<\/span> <\/span><iostream><\/span><\/span>\n<\/span>\nclass<\/span> <\/span>Person<\/span><\/span>\n{<\/span><\/span>\npublic:<\/span><\/span>\n  \/\/ Constructor<\/span><\/span>\n  <\/span>Person<\/span>(<\/span>const<\/span> <\/span>std<\/span>::<\/span>string<\/span> <\/span>&<\/span>nm<\/span>,<\/span><\/span>\n         <\/span>const<\/span> <\/span>std<\/span>::<\/span>string<\/span> <\/span>&<\/span>street<\/span> = <\/span>""<\/span>, <\/span><\/span>\n         <\/span>const<\/span> <\/span>std<\/span>::<\/span>string<\/span> <\/span>&<\/span>town<\/span> = <\/span>""<\/span>,<\/span><\/span>\n         <\/span>const<\/span> <\/span>std<\/span>::<\/span>string<\/span> <\/span>&<\/span>state<\/span> = <\/span>""<\/span>,<\/span><\/span>\n         <\/span>int<\/span> <\/span>a<\/span> = -<\/span>1<\/span>);<\/span><\/span>\n  <\/span><\/span>\n  \/\/ Access member functions<\/span><\/span>\n  <\/span>const<\/span> <\/span>std<\/span>::<\/span>string<\/span> <\/span>&<\/span>getName<\/span>() <\/span>const<\/span> { <\/span>return<\/span> m_name; }<\/span><\/span>\n  <\/span>const<\/span> <\/span>std<\/span>::<\/span>string<\/span> <\/span>&<\/span>getStreet<\/span>() <\/span>const<\/span> { <\/span>return<\/span> m_street; }<\/span><\/span>\n  <\/span>const<\/span> <\/span>std<\/span>::<\/span>string<\/span> <\/span>&<\/span>getTown<\/span>() <\/span>const<\/span> { <\/span>return<\/span> m_town; }<\/span><\/span>\n  <\/span>const<\/span> <\/span>std<\/span>::<\/span>string<\/span> <\/span>&<\/span>getState<\/span>() <\/span>const<\/span> { <\/span>return<\/span> m_state; }<\/span><\/span>\n  <\/span>const<\/span> <\/span>int<\/span> <\/span>getAge<\/span>() <\/span>const<\/span> { <\/span>return<\/span> m_age; }<\/span><\/span>\n  <\/span><\/span>\n  \/\/ Mutator member functions<\/span><\/span>\n  <\/span>void<\/span> <\/span>setStreet<\/span>(<\/span>const<\/span> <\/span>std<\/span>::<\/span>string<\/span> <\/span>&<\/span>street<\/span>) { m_street = street; }<\/span><\/span>\n  <\/span>void<\/span> <\/span>setTown<\/span>(<\/span>const<\/span> <\/span>std<\/span>::<\/span>string<\/span> <\/span>&<\/span>town<\/span>) { m_town = town; }<\/span><\/span>\n  <\/span>void<\/span> <\/span>setState<\/span>(<\/span>const<\/span> <\/span>std<\/span>::<\/span>string<\/span> <\/span>&<\/span>state<\/span>) { m_state = state; }<\/span><\/span>\n  <\/span>void<\/span> <\/span>setAge<\/span>(<\/span>int<\/span> <\/span>age<\/span>) { m_age = age; }<\/span><\/span>\n  <\/span><\/span>\n  <\/span>friend<\/span><\/span>\n  <\/span>std<\/span>::<\/span>ostream<\/span> <\/span>&<\/span>operator<<<\/span>(<\/span>std<\/span>::<\/span>ostream<\/span> <\/span>&<\/span>os<\/span>, <\/span>const<\/span> <\/span>Person<\/span> <\/span>&<\/span>p<\/span>);<\/span><\/span>\n  <\/span><\/span>\n  <\/span>friend<\/span><\/span>\n  <\/span>std<\/span>::<\/span>istream<\/span> <\/span>&<\/span>operator>><\/span>(<\/span>std<\/span>::<\/span>istream<\/span> <\/span>&<\/span>is<\/span>, <\/span>Person<\/span> <\/span>&<\/span>p<\/span>);<\/span><\/span>\n<\/span>\nprivate:<\/span><\/span>\n  <\/span>std<\/span>::string m_name;<\/span><\/span>\n  <\/span>std<\/span>::string m_street;<\/span><\/span>\n  <\/span>std<\/span>::string m_town;<\/span><\/span>\n  <\/span>std<\/span>::string m_state;<\/span><\/span>\n  <\/span>int<\/span>  m_age;<\/span><\/span>\n};<\/span><\/span>\n<\/span>\n#endif<\/span> \/* Person_h *\/<\/span><\/span><\/code><\/pre><\/div>\n\n\n\n
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Note how more complex the code is for input compared with output. 
I don’t claim this is particularly efficient, and it clearly doesn’t scale as a solution (if we had lots more fields. etc.)<\/p>\n<\/blockquote>\n<\/div>\n\n\n\n
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<\/path><\/path><\/svg><\/span>
\/\/<\/span><\/span>\n\/\/  Person.cpp<\/span><\/span>\n\/\/  iostreams - User-defined types<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 9\/4\/24.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#include<\/span> <\/span>"Person.h"<\/span><\/span>\n#include<\/span> <\/span><iostream><\/span><\/span>\n<\/span>\n\/\/ Constructor<\/span><\/span>\nPerson<\/span>::<\/span>Person<\/span>(<\/span>const<\/span> <\/span>std<\/span>::string &name,<\/span><\/span>\n       <\/span>const<\/span> <\/span>std<\/span>::string &street,<\/span><\/span>\n       <\/span>const<\/span> <\/span>std<\/span>::string &town,<\/span><\/span>\n       <\/span>const<\/span> <\/span>std<\/span>::string &state,<\/span><\/span>\n       <\/span>int<\/span> age)<\/span><\/span>\n  : <\/span>m_name<\/span>(name), <\/span>m_street<\/span>(street), <\/span>m_town<\/span>(town),<\/span><\/span>\n    <\/span>m_state<\/span>(state), <\/span>m_age<\/span>(age)<\/span><\/span>\n{ }<\/span><\/span>\n<\/span>\nstatic<\/span> <\/span>const<\/span> <\/span>char<\/span> NAME[]  = <\/span>"Name:   "<\/span>;<\/span><\/span>\nstatic<\/span> <\/span>const<\/span> <\/span>char<\/span> STREET[]  = <\/span>"Street: "<\/span>;<\/span><\/span>\nstatic<\/span> <\/span>const<\/span> <\/span>char<\/span> TOWN[]  = <\/span>"Town:   "<\/span>;<\/span><\/span>\nstatic<\/span> <\/span>const<\/span> <\/span>char<\/span> STATE[]  = <\/span>"State:  "<\/span>;<\/span><\/span>\nstatic<\/span> <\/span>const<\/span> <\/span>char<\/span> AGE[]  = <\/span>"Age:    "<\/span>;<\/span><\/span>\n<\/span>\n<\/span>\n\/\/ Overloaded operator <<<\/span><\/span>\nstd<\/span>::<\/span>ostream<\/span> <\/span>&<\/span>operator<<<\/span>(<\/span>std<\/span>::<\/span>ostream<\/span> <\/span>&<\/span>os<\/span>, <\/span>const<\/span> <\/span>Person<\/span> <\/span>&<\/span>p<\/span>)<\/span><\/span>\n{<\/span><\/span>\n  <\/span>return<\/span> os << NAME << <\/span>p<\/span>.<\/span>m_name<\/span> << <\/span>std<\/span>::endl<\/span><\/span>\n            << STREET << <\/span>p<\/span>.<\/span>m_street<\/span> << <\/span>std<\/span>::endl<\/span><\/span>\n            << TOWN << <\/span>p<\/span>.<\/span>m_town<\/span> << <\/span>std<\/span>::endl<\/span><\/span>\n            << STATE << <\/span>p<\/span>.<\/span>m_state<\/span> << <\/span>std<\/span>::endl<\/span><\/span>\n            << AGE << <\/span>p<\/span>.<\/span>m_age<\/span> << <\/span>std<\/span>::endl;<\/span><\/span>\n}<\/span><\/span>\n<\/span>\n\/\/ Overloaded operator >><\/span><\/span>\nstd<\/span>::<\/span>istream<\/span> <\/span>&<\/span>operator>><\/span>(<\/span>std<\/span>::<\/span>istream<\/span> <\/span>&<\/span>is<\/span>, <\/span>Person<\/span> <\/span>&<\/span>p<\/span>)<\/span><\/span>\n{<\/span><\/span>\n  <\/span>static<\/span> <\/span>char<\/span> <\/span>buffer<\/span>[<\/span>81<\/span>];<\/span><\/span>\n  <\/span>static<\/span> <\/span>char<\/span> <\/span>value<\/span>[<\/span>81<\/span>];<\/span><\/span>\n<\/span>\n  <\/span>is<\/span>.<\/span>get<\/span>(buffer, <\/span>sizeof<\/span>(NAME));<\/span> \/\/ Read the label<\/span><\/span>\n  <\/span>is<\/span>.<\/span>get<\/span>(value, <\/span>sizeof<\/span>(value));<\/span> \/\/ Read the value<\/span><\/span>\n  <\/span>p<\/span>.<\/span>m_name<\/span> = value;<\/span><\/span>\n  <\/span>is<\/span>.<\/span>getline<\/span>(buffer, <\/span>sizeof<\/span>(buffer));<\/span> \/\/ Discard the newline<\/span><\/span>\n  <\/span><\/span>\n  <\/span>is<\/span>.<\/span>get<\/span>(buffer, <\/span>sizeof<\/span>(STREET));<\/span><\/span>\n  <\/span>is<\/span>.<\/span>get<\/span>(value, <\/span>sizeof<\/span>(value));<\/span><\/span>\n  <\/span>p<\/span>.<\/span>m_street<\/span> = value;<\/span><\/span>\n  <\/span>is<\/span>.<\/span>getline<\/span>(buffer, <\/span>sizeof<\/span>(buffer));<\/span><\/span>\n  <\/span><\/span>\n  <\/span>is<\/span>.<\/span>get<\/span>(buffer, <\/span>sizeof<\/span>(TOWN));<\/span><\/span>\n  <\/span>is<\/span>.<\/span>get<\/span>(value, <\/span>sizeof<\/span>(value));<\/span><\/span>\n  <\/span>p<\/span>.<\/span>m_town<\/span> = value;<\/span><\/span>\n  <\/span>is<\/span>.<\/span>getline<\/span>(buffer, <\/span>sizeof<\/span>(buffer));<\/span><\/span>\n<\/span>\n  <\/span>is<\/span>.<\/span>get<\/span>(buffer, <\/span>sizeof<\/span>(STATE));<\/span><\/span>\n  <\/span>is<\/span>.<\/span>get<\/span>(value, <\/span>sizeof<\/span>(value));<\/span><\/span>\n  <\/span>p<\/span>.<\/span>m_state<\/span> = value;<\/span><\/span>\n  <\/span>is<\/span>.<\/span>getline<\/span>(buffer, <\/span>sizeof<\/span>(buffer));<\/span><\/span>\n<\/span>\n  <\/span>is<\/span>.<\/span>get<\/span>(buffer, <\/span>sizeof<\/span>(AGE));<\/span><\/span>\n  is >> <\/span>p<\/span>.<\/span>m_age<\/span>;<\/span><\/span>\n  <\/span>is<\/span>.<\/span>getline<\/span>(buffer, <\/span>sizeof<\/span>(buffer));<\/span><\/span>\n<\/span>\n  <\/span>return<\/span> is;<\/span><\/span>\n}<\/span><\/span><\/code><\/pre><\/div>\n<\/div>\n<\/div>\n\n\n\n
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… and here’s a main program to test it:<\/p>\n\n\n\n
<\/path><\/path><\/svg><\/span>
\/\/<\/span><\/span>\n\/\/  main.cpp<\/span><\/span>\n\/\/  iostreams - User-defined types<\/span><\/span>\n\/\/<\/span><\/span>\n\/\/  Created by Bryan Higgs on 9\/4\/24.<\/span><\/span>\n\/\/<\/span><\/span>\n<\/span>\n#include<\/span> <\/span><iostream><\/span><\/span>\n#include<\/span> <\/span>"Person.h"<\/span><\/span>\n<\/span>\nint<\/span> <\/span>main<\/span>(<\/span>int<\/span> <\/span>argc<\/span>, <\/span>const<\/span> <\/span>char<\/span> <\/span>*<\/span> <\/span>argv<\/span>[]) <\/span><\/span>\n{<\/span><\/span>\n  Person <\/span>p1<\/span>(<\/span>""<\/span>), <\/span>p2<\/span>(<\/span>""<\/span>);<\/span><\/span>\n<\/span>\n  <\/span>std<\/span>::cout << <\/span>"Enter data for Person 1:"<\/span> << <\/span>std<\/span>::endl;<\/span><\/span>\n  <\/span>std<\/span>::cin >> p1;<\/span><\/span>\n  <\/span>std<\/span>::cout << <\/span>"Enter data for Person 2:"<\/span> << <\/span>std<\/span>::endl;<\/span><\/span>\n  <\/span>std<\/span>::cin >> p2;<\/span><\/span>\n<\/span>\n  <\/span>std<\/span>::cout << <\/span>"<\/span>\\n<\/span>+++Person 1++++"<\/span> << <\/span>std<\/span>::endl << p1;<\/span><\/span>\n  <\/span>std<\/span>::cout << <\/span>"<\/span>\\n<\/span>+++Person 2++++"<\/span> << <\/span>std<\/span>::endl << p2;<\/span><\/span>\n<\/span>\n  <\/span>return<\/span> <\/span>0<\/span>;<\/span><\/span>\n}<\/span><\/span><\/code><\/pre><\/div>\n<\/div>\n\n\n\n
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It outputs:<\/p>\n\n\n\n
Enter data for Person 1:\nName:   Fred Bloggs\nStreet: 15 Highland Terrace\nTown:   Cleveland\nState:  OH\nAge:    34<\/em><\/code>\n\nEnter data for Person 2:\nName:   Mary Smith\nStreet: 27 Doubleday Ave.\nTown:   Monterey\nState:  CA\nAge:    28<\/em><\/code>\n\n\n+++Person 1++++\nName:   Fred Bloggs\nStreet: 15 Highland Terrace\nTown:   Cleveland\nState:  OH\nAge:    34\n\n+++Person 2++++\nName:   Mary Smith\nStreet: 27 Doubleday Ave.\nTown:   Monterey\nState:  CA\nAge:    28\nProgram ended with exit code: 0<\/code><\/pre>\n\n\n\n
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The italicized text<\/em> was input to the program.
Note that I simply copied the output from the earlier program, and pasted it in for input. (You don’t want to do this manually, as it is very picky to get right!)<\/p>\n<\/blockquote>\n<\/div>\n<\/div>\n\n\n\n
<\/div>\n\n\n\n
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Next: Writing Your Own Stream Manipulators<\/a><\/div>\n<\/div>\n","protected":false},"excerpt":{"rendered":"
Input of User-Defined Types Input may be defined in a similar way: But it’s a little trickier on input, because you have to get the formatting exactly right (just as scanf() is trickier to use than printf() in C). Example Let’s assume that we wish to read back the exact same stuff we output before […]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":936,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-1863","page","type-page","status-publish","hentry"],"blocksy_meta":[],"_links":{"self":[{"href":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/wp-json\/wp\/v2\/pages\/1863","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/wp-json\/wp\/v2\/comments?post=1863"}],"version-history":[{"count":3,"href":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/wp-json\/wp\/v2\/pages\/1863\/revisions"}],"predecessor-version":[{"id":1888,"href":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/wp-json\/wp\/v2\/pages\/1863\/revisions\/1888"}],"up":[{"embeddable":true,"href":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/wp-json\/wp\/v2\/pages\/936"}],"wp:attachment":[{"href":"https:\/\/bhiggs.x10hosting.com\/PracticalCPlusPlusProgramming\/index.php\/wp-json\/wp\/v2\/media?parent=1863"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}