I'm sure this is a really simple thing, but I haven't worked in C++ forever.
14 C:\Dev-Cpp\mainCurl.cpp `string'
undeclared (first use this function)
> #include <stdio.h>
> #include <curl/curl.h>
> #include <string>
> #include <iostream>
>
> int main(void) {
> string url("http://www.google.com"); //
> system("pause");
>
> return 0; }
What am I missing here?
Cheers
You haven't declared your namespace. You need to either declare:
using namespace std;
Or tell the compiler that "string" is in the standard namespace:
std::string url("...");
Or you can announce that you are specifically using std::string and only std::string from std by saying:
using std::string;
Add using namespace std; above the main() definition.
Also, you don't need <stdio.h> if you include <iostream>. Also, in C++ a function that doesn't take arguments doesn't need a "void" argument, simply use parentheses with nothing in between them.
This a so recurring problem...
You missed std:: before string, so it will look like std::string
That's because string belongs to std namespace and if you don't use using directive you must specify where string is.
Alternatively you can use
using namespace std; or more conveniently using std::string before using string class.
You need std::string or using std::string.
try std::string url ("http://www.google.com");
the string class is in std namespace
Related
I have the following code:
#include <string>
#include <boost/thread/tss.hpp>
static boost::thread_specific_ptr<string> _tssThreadNameSptr;
I get the following error
g++ -c -I$BOOST_PATH tssNaming.h
tssNaming.h:7: error: 'string' was not declared in this scope
But I am including string in my #include.
You have to use std::string since it's in the std namespace.
string is in the std namespace. You have the following options:
Write using namespace std; after the include and enable all the std names: then you can write only string on your program.
Write using std::string after the include to enable std::string: then you can write only string on your program.
Use std::string instead of string
I find that including:
using namespace std;
To your C++ code saves a lot of time in debugging especially in situations like yours where std:: string is required and also it will help in keeping your code clean.
With this in mind, your code should be:
#include <string>
using namespace std;
#include <boost/thread/tss.hpp>
static boost::thread_specific_ptr<string> _tssThreadNameSptr;
I can't declare a string in my program:
string MessageBoxText = CharNameTextBox->Text;
it just doesn't work. It says string is undeclared identifier. What am I missing in the namespace or include or something like that?
Make sure you've included this header:
#include <string>
And then use std::string instead of string. It is because string is defined in std namespace.
And don't write this at namespace scope:
using namespace std; //bad practice if you write this at namespace scope
However, writing it at function scope is not that bad. But the best is one which I suggested before:
Use std::string as:
std::string MessageBoxText = CharNameTextBox->Text;
To use the standard string class in C++ you need to #include <string>. Once you've added the #include directive string will be defined in the std namespace and you can refer to it as std::string.
E.g.
#include <string>
#include <iostream>
int main()
{
std::string hw( "Hello, world!\n" );
std::cout << hw;
return 0;
}
Are you by any way compiling using C++/CLI, the Microsoft extension for .NET, and not standard ISO C++?
In that case you should do the following:
System::String^ MessageBoxText = CharNameTextBox->Text;
Also see the following articles:
How to: Convert Between Various String Types
How to: Convert System::String to Standard String
How to: Convert Standard String to System::String
I am receiving the error: identifier "string" undefined.
However, I am including string.h and in my main file, everything is working fine.
CODE:
#pragma once
#include <iostream>
#include <time.h>
#include <string.h>
class difficulty
{
private:
int lives;
string level;
public:
difficulty(void);
~difficulty(void);
void setLives(int newLives);
int getLives();
void setLevel(string newLevel);
string getLevel();
};
Can someone please explain to me why this is occurring?
<string.h> is the old C header. C++ provides <string>, and then it should be referred to as std::string.
You want to do #include <string> instead of string.h and then the type string lives in the std namespace, so you will need to use std::string to refer to it.
You forgot the namespace you're referring to. Add
using namespace std;
to avoid std::string all the time.
Because string is defined in the namespace std. Replace string with std::string, or add
using std::string;
below your include lines.
It probably works in main.cpp because some other header has this using line in it (or something similar).
Perhaps you wanted to #include<string>, not <string.h>. std::string also needs a namespace qualification, or an explicit using directive.
You must use std namespace. If this code in main.cpp you should write
using namespace std;
If this declaration is in header, then you shouldn't include namespace and just write
std::string level;
#include <string> would be the correct c++ include, also you need to specify the namespace with std::string or more generally with using namespace std;
does this work on string in c++?
string s="lomi";
cout<<s<<endl;
what is bad in this code?
#include <iostream>
#include <cstring>
using namespace std;
int main(){
string s=string("lomi");
for (int i=0;i<s.length();i++){
s[i]= s[i]+3;
}
std::cout<<s<<std::endl;
return 0;
}
?
Yes.
(after you have #included the corresponding headers, and using the std namespace, etc.)
Edit: What's wrong with your code is you should
#include <string>
instead of
#include <cstring>
cstring is C's string.h header, which defines functions like strlen, strcpy, etc. that manipulates a C string, i.e. char*.
string defines C++'s string class which you're using.
short answer: yes
long answer: string s = "lomi"works due to the string(const char*) constructor.
Works for me -- does it work for you?
Remember to do this first:
#include <ostream>
#include <string>
using namespace std;
yes, cout in C++ knows how to deal with strings
Yes it should compile and work, if you want to print "lomi\n", and you have included <string> and <ostream> and declared using namespace std;.
I know this is quite a ridiculous question but this is quite confusing and irritating, as something that should work simply is not. I'm using Code Blocks with the GCC compiler and I am trying to simply create a string variable in my class
#ifndef ALIEN_LANGUAGE
#define ALIEN_LANGUAGE
#include <string>
class Language
{
public:
private:
string str;
};
#endif
Strange enough, my compiler halts me with an error saying this:
C:\Documents and Settings\...|11|error: `string' does not name a type|
||=== Build finished: 1 errors, 0 warnings ===|
For some reason, it is unable to find the class "string" which for some reason, my main.cpp is able to detect "#include " while my language class is not able for some reason.
This is the main I wrote quickly just to see it main itself is able to see the string file:
//main.cpp
#include <iostream>
#include <string>
#include "alien_language.h"
using namespace std;
int main()
{
string str;
return 0;
}
Does anyone know what's going on?
using namespace std;
That's what's going on.
You don't have std:: prefixing the string in your class. Everything in the standard library is in the namespace std.
It is generally regarded as bad practice to use using namespace std;, by the way. For more information on why and what to do instead, check out this question: Using std Namespace.
The string class is defined in the std namespace. You should chenge the class to this:
class Language
{
public:
private:
std::string str;
};
It is also possible, but not recommended to add this to the top of the header file:
using namespace std;
string is in namespace std, and you need to qualify it fully inside your header file:
#include <string>
class Language
{
public:
private:
std::string str;
};
Do not use using namespace std; or similar in header files.
You should refer to it as std::string;
It looks to me like you're missing the all-important (with a hint of sarcasm) using namespace std; line. Either add that in before your class, or explicitely use std::string str. I'd recommend against adding the using namespace std; line in a header file, as it would pollute the mainspace for any file that includes it.
The string class in standard C++ is in std namespace. Write something like
using std::string; in your header or fully qualify it as std::string in your header.
Beware that using namespace std; in header is a bad practice (read here).