how to understand cpp compiler g++ error message.

[white vessel]

I did java, then i did c, both have easy bug message, but that's not true for cpp.
Even if I do cin << instead of cin >> . This will produce error message so much, i can't understand the issue. I have to guess from line number.
Same today I forgot to initialise virtual function, it gave a weird message instead of simply telling me that.

Any why is that???

[eager rampart]

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[brave chasm]

;compile cpp

#include <iostream>
int main() {
    std::cin>>2;
}

[magic moat]

Compiler Output

<source>: In function 'int main()':
<source>:3:13: error: no match for 'operator>>' (operand types are 'std::istream' {aka 'std::basic_istream<char>'} and 'int')
    3 |     std::cin>>2;
      |     ~~~~~~~~^~~
      |          |    |
      |          |    int
      |          std::istream {aka std::basic_istream<char>}
In file included from /opt/compiler-explorer/gcc-12.2.0/include/c++/12.2.0/iostream:40,
                 from <source>:1:
/opt/compiler-explorer/gcc-12.2.0/include/c++/12.2.0/istream:120:7: note: candidate: 'std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(__istream_type& (*)(__istream_type&)) [with _CharT = char; _Traits = std::char_traits<char>; __istream_type = std::basic_istream<char>]' (near match)
  120 |       operator>>(__istream_type& (*__pf)(__istream_type&))
      |       ^~~~~~~~
/opt/compiler-explorer/gcc-12.2.0/include/c++/12.2.0/istream:120:7: note:   conversion of argument 1 would be ill-formed:
<sou

jr-#6677 | c++ | x86-64 gcc 12.2 | godbolt.org

[brave chasm]

https://godbolt.org/z/hsq9xWThe

Start at the top

<source>: In function 'int main()':
<source>:3:13: error: no match for 'operator>>' (operand types are 'std::istream' {aka 'std::basic_istream<char>'} and 'int')
    3 |     std::cin>>2;
      |     ~~~~~~~~^~~
      |          |    |
      |          |    int
      |          std::istream {aka std::basic_istream<char>}

Always start at the top

This tells you where the problem is and the immediate reason why

https://godbolt.org/z/4vTh3WqhM

same here

<source>: In function 'int main()':
<source>:3:13: error: no match for 'operator<<' (operand types are 'std::istream' {aka 'std::basic_istream<char>'} and 'int')
    3 |     std::cin<<2;
      |     ~~~~~~~~^~~
      |          |    |
      |          |    int
      |          std::istream {aka std::basic_istream<char>}

Compiler can't find a way to perform that operator

All the other lines, and there are a daunting number of errors yes, contain information about what the compiler tried and was unable to do

It goes through all the overload candidates and provides information about why each one does not apply here

[eager rampart]

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