Wednesday 21 August 2019
c++ - 'list' was not declared in this scope
Answer
Answer
I am new to c++, and I am trying to get a basic program to initialize a list of short unsigned integers. I am compiling and running using scygwin and g++.
Below is the code in the .cpp file:
#include
#include
#include
#include
#include
using namespace std;
int main (int argc, char* argv[]) {
list events;
return 0;
}
which I run by typing the following command into cygwin terminal:
$ g++ -o test.out test.cpp
However, I get the following compilation errors:
test.cpp: In function ‘int main(int, char**)’: test.cpp:16:1: error:
‘list’ was not declared in this scope list events;
^
test.cpp:16:6: error: expected primary-expression before ‘int’
list events;
^
I am confused about why list is not in the scope, since I am using namespace std? I found a similar question asked about this on a c++ forum, but my problem would be resolved with that. Anyone know what the problem is here?
-Paul
Answer
using namespace std;
doesn't add any functionality to your code. It just means you don't have to type std::
when referencing things in the std
namespace, like std::list
.
To actually include the code base for std::list
into your program, you need to add:
#include
When in doubt about this kind of thing, doing a google search for cpp reference list
will turn up a page like this where you can see: Defined in header
at the top.
Here's another question about using namespace std;
that may prove useful and why you shouldn't use it. I'll add a little bit to perhaps explain namespaces.
It is common in C++ programs to organize functions into classes and namespaces. Imagine you wrote your own list
class to handle certain scenarios. In order to prevent naming conflicts you would put it in a different namespace than std
.
namespace MyApp {
class list;
void sort(list&);
}
For the majority of a large code base you might still prefer to use std::list
but you need MyApp::list
for some things. Using namespaces you can cluster your code and prevent naming conflicts for similar functionality.
Summary
using namespace std;
makes it so that if you reference a function or class not in the global namespace it looks for it in the std
namespace.
#include
actually inserts prototypes (information about how to access the code) in your source file during the preprocessor stage.
php - file_get_contents shows unexpected output while reading a file
I want to output an inline jpg image as a base64 encoded string, however when I do this : $contents = file_get_contents($filename); print &q...
-
I have an app which needs a login and a registration with SQLite. I have the database and a user can login and register. But i would like th...
-
I would like to use enhanced REP MOVSB (ERMSB) to get a high bandwidth for a custom memcpy . ERMSB was introduced with the Ivy Bridge micro...
-
According to my understanding, and my calculator, cos(90 degrees) equals 0 . In my code, I have a funct...
No comments:
Post a Comment