I'm trying to run my very first c++ program in linux (linux mint 8). I use either gcc or g++, both with the same problem: the compiler does not find the library I am trying to import.
I suspect something like I should either copy the iostream.h file (which I don't know where to look for) in the working folder, move my file to compile somewhere else or use an option of some sort.
Thanks for your suggestions.
Here's the gcc command, the c++ code, and the error message:
gcc -o addition listing2.5.c
.
#include <iostream.h>
int Addition(int a, int b)
{
return (a + b);
}
int main()
{
cout << "Resultat : " << Addition(2, 4) << "\n";
return 0;
}
.
listing2.5.c:1:22: error: iostream.h: No such file or directory
listing2.5.c: In function ‘main’:
listing2.5.c:10: error: ‘cout’ undeclared (first use in this function)
listing2.5.c:10: error: (Each undeclared identifier is reported only once
listing2.5.c:10: error: for each function it appears in.)
Now the code compiles, but I cannot run it from the command line using the file name. addition: command not found Any suggestion?
cout is defined in the std:: namespace, you need to use std::cout instead of just cout.
You should also use #include <iostream> not the old iostream.h
use g++ to compile C++ programs, it'll link in the standard c++ library. gcc will not. gcc will also compile your code as C code if you give it a .c suffix. Give your files a .cpp suffix.
please use g++ not gcc to compile it
You need <iostream> not <iostream.h>.
They are also header files not libraries.
Other things to fix, cout should be std::cout and you should use std::endl instead of "\n".
You need <iostream>, <iostream.h> is non-standard too-old header. Try this:
#include <iostream>
int Addition(int a, int b)
{
return (a + b);
}
int main()
{
using namespace std;
cout << "Resultat : " << Addition(2, 4) << "\n";
return 0;
}
If you don't want to use std alongside cout as below-
std::cout << "Hello World";
You can also define std at beginning of program by 'using namespace' keywords as-
#include <iostream >
using namespace std;
int Addition(int a, int b)
{
return (a + b);
}
int main()
{
cout << "Result : " << Addition(2, 4) << "\n";
return 0;
}
Now you need not to write std,everytime you use I/O operations.
Related
I am trying out a simple program to print the timestamp value of steady_clock as shown below:
#include <iostream>
#include <chrono>
using namespace std;
int main ()
{
cout << "Hello World! ";
uint64_t now = duration_cast<milliseconds>(steady_clock::now().time_since_epoch()).count();
cout<<"Value: " << now << endl;
return 0;
}
But whenever I am compiling like this g++ -o abc abc.cpp, I am always getting an error:
In file included from /usr/include/c++/4.6/chrono:35:0,
from abc.cpp:2:
/usr/include/c++/4.6/bits/c++0x_warning.h:32:2: error: #error This file requires compiler and library support for the upcoming ISO C++ standard, C++0x. This support is currently experimental, and must be enabled with the -std=c++0x or -std=gnu++0x compiler options.
abc.cpp: In function âint main()â:
abc.cpp:7:3: error: âuint64_tâ was not declared in this scope
abc.cpp:7:12: error: expected â;â before ânowâ
abc.cpp:8:22: error: ânowâ was not declared in this scope
Is there anything wrong I am doing?
Obviously, I'm not following certain best practices, but just trying to get things working for you
#include <iostream>
#include <chrono>
#include <cstdint> // include this header for uint64_t
using namespace std;
int main ()
{
{
using namespace std::chrono; // make symbols under std::chrono visible inside this code block
cout << "Hello World! ";
uint64_t now = duration_cast<milliseconds>(steady_clock::now().time_since_epoch()).count();
cout<<"Value: " << now << endl;
}
return 0;
}
and then compile using C++11 enabled (c++0x in your case)
g++ -std=c++0x -o abc abc.cpp
You should include stdint.h file.
If you really want to include, add "#define __STDC_LIMIT_MACROS"
Ref: https://stackoverflow.com/a/3233069/6728794
Here's the code....
#include <iostream>
int main()
{
cout << "WELCOME TO C++ PROGRAMMING";
return 0;
}
And when I go the terminal and pass the command..
g++ hello.cpp
It shows...
hello.cpp: In function ‘int main()’:
hello.cpp:4:2: error: ‘cout’ was not declared in this scope
cout << "WELCOME TO C++ PROGRAMMING";
^
hello.cpp:4:2: note: suggested alternative:
In file included from hello.cpp:1:0:
/usr/include/c++/4.8/iostream:61:18: note: ‘std::cout’
extern ostream cout; /// Linked to standard output
So what's the reason? And what should I do?
cout is found in the std namespace.
#include <iostream>
int main()
{
std::cout << "Welcome";
return 0;
}
To avoid name collisions, the C++ library is included in a namespace, named std. So to get your program to compile, either you add:
using namespace std;
at the top of your program, either you prefix each "object" of the standard library with std:::
std::cout << "Welcome";
You should use std before cout
You should have:
std::cout << "Welcome";
So, I have the following code, and it builds and runs perfectly, tried various values and all is well. You'll notice I use log10 function and I do not include cmath or math.h. Why does it still build and run fine? Are those libraries really needed? Why/Why not? Does it have anything to do with me using visual studio? Like, would it not compile if say I was using a different IDE or command prompt to compile it?
#include <iostream>
#include <iomanip>
using namespace std;
int main() {
cout << "Classify solutions as acidic or nonacidic" << endl<< endl;
//declaring double molar concentration
double mc = 1;
//using while and if statements to calculate pH in fixed notaion and acidic or nonacidic
while (mc != 0)
{
cout << "Please enter a molar concentration (or enter 0 to exit): ";
cin >> mc;
if (mc != 0)
{
cout << "Molar Conentration = " << scientific << mc << endl; //scientific notation
double pH = -log10(mc);
cout << "pH = " << fixed << setprecision(6) << pH << endl; //6 deciumals
if (pH > 7)
{
cout << "Nonacidic" << endl << endl;
}
else if (pH < 7)
{
cout << "Acidic" << endl << endl;
}
else
cout << "Neutral" << endl << endl;
}
}
//end program when inputing 0
cout << "End of Program" << endl;
return 0;
}
The code:
i = i++ + ++i;
may also compile okay, but that doesn't make it a good idea :-)
It would be wise to include headers for library functions that you use. You don't lose any functionality by doing so but you do guarantee the functionality will work (misuse notwithstanding).
Detailed analysis follows.
Even if an implementation is relaxed about this, the standard mandates it. C++11 17.6.2.2 Headers /3 states:
A translation unit shall include a header only outside of any external declaration or definition, and shall include the header lexically before the first reference in that translation unit to any of the entities declared in that header.
The gcc compiler, for example, will grumble bitterly about your code:
xyzzy.cpp: In function 'int main()':
xyzzy.cpp:22:34: error: 'log10' was not declared in this scope
double pH = -log10(mc);
^
As to why VC++ seemingly violates this rule, it has to do with the fact that header files are allowed to include other header files.
If you compile your code to produce pre-processor output (with /P), you'll find a line buried deep within it thus (at least in VS2013):
#line 1 "c:\\blah\\blah\\vc\\include\\cmath"
And a bit of analysis turns up the following hierarchy of includes:
iostream
istream
ostream
ios
xlocnum
cmath
(<xlocnum>, one of the internal headers used by <locale>, appears to need ldexp() from the <cmath> library, though there may be others as well).
That's further evidenced by the fact that VC++ does complain about the following code:
//#include <iostream>
using namespace std;
int main() {
double oneHundred = 100;
int two = log10 (oneHundred);
return two;
}
with:
error C3861: 'log10': identifier not found
but that error disappears the instant you uncomment the iostream inclusion line.
However, as previously stated, that is not behaviour you should rely on. If you are going to use a library function (or macro/template/whatever), it's up to you to include the correct header.
Otherwise your program compiling correctly is simply an accident.
As you've noticed, the code snippet you provided works in Visual Studio but not with other compilers. This is because of how the standard library is implemented for each compiler.
It turns out that when you include Visual Studio's implementation of <iostream>, you end up including a bunch of other headers indirectly, and one of these headers is <cmath>.
To see the exact chain, navigate to the standard library include directory. For me (I use Visual Studio 2013 Community Edition) this is located at
C:\Program Files (x86)\Microsoft Visual Studio 12.0\VC\include
Open iostream. Note the line #include <istream>
Open istream. Note the line #include <ostream>
Open ostream. Note the line #include <ios>
Open ios. Note the line #include <xlocnum>
Open xlocnum. Note the line #include <cmath>
Guess what? You included cmath when you included iostream... so your code is good to go, on Visual Studio at least. But, don't rely on implementation details or your code will break if you try to migrate it to another platform/toolchain.
For example, trying to compile the provided snippet using g++ on Cygwin results in the following error:
temp.cpp: In function ‘int main()’:
temp.cpp:22:34: error: ‘log10’ was not declared in this scope
double pH = -log10(mc);
This must mean g++'s implementation of <iostream> doesn't depend on <cmath>
When using the double variant of the std::abs() function without the std with g++ 4.6.1, no warning or error is given.
#include <algorithm>
#include <cmath>
double foobar(double a)
{
return abs(a);
}
This version of g++ seems to be pulling in the double variant of abs() into the global namespace through one of the includes from algorithm. This looks like it is now allowed by the standard (see this question), but not required.
If I compile the above code using a compiler that does not pull the double variant of abs() into the global namespace (such as g++ 4.2), then the following error is reported:
warning: passing 'double' for argument 1 to 'int abs(int)'
How can I force g++ 4.6.1, and other compilers that pull functions into the global namespace, to give a warning so that I can prevent errors when used with other compilers?
The function you are using is actually the integer version of abs, and GCC does an implicit conversion to integer.
This can be verified by a simple test program:
#include <iostream>
#include <cmath>
int main()
{
double a = -5.4321;
double b = std::abs(a);
double c = abs(a);
std::cout << "a = " << a << ", b = " << b << ", c = " << c << '\n';
}
Output is:
a = -5.4321, b = 5.4321, c = 5
To get a warning about this, use the -Wconversion flag to g++. Actually, the GCC documentation for that option explicitly mentions calling abs when the argument is a double. All warning options can be found here.
Be warned, you don't need to explicitly #include <cmath>, <iostream> does the damage as well (and maybe some other headers). Also, note that -Wall doesn't give you any warnings about it.
#include <iostream>
int main() {
std::cout << abs(.5) << std::endl;
std::cout << typeid(decltype(abs)).name() << std::endl;
}
Gives output
0
FiiE
On
gcc version 7.4.0 (Ubuntu 7.4.0-1ubuntu1~18.04)
I am new to C++ programming.
So I was trying my luck executing some small programs.
I am working on HP-UX which has a compiler whose
executable is named aCC.
I am trying to execute a small program
#include <iostream.h>
using namespace std;
class myclass {
public:
int i, j, k;
};
int main()
{
myclass a, b;
a.i = 100;
a.j = 4;
a.k = a.i * a.j;
b.k = 12;
cout << a.k << " " << b.k;
return 0;
}
When I compile this it gives me an error:
> aCC temp.cpp
Error 697: "temp.cpp", line 2 # Only namespace names are valid here.
using namespace std;
^^^
What exactly is the problem?
Is std not considered as a namespace in the aCC compiler or is there some serious drawback with aCC?
If I change the <iostream.h> to <iostream>, I get some more errors added as below.
>aCC temp.cpp
Error 112: "temp.cpp", line 1 # Include file <iostream> not found.
#include <iostream>
^^^^^^^^^^
Error 697: "temp.cpp", line 2 # Only namespace names are valid here.
using namespace std;
^^^
Error 172: "temp.cpp", line 14 # Undeclared variable 'cout'.
cout << a.k << " " << b.k;
Which version of aCC are you using? Older versions used a pre-standard STL implemenntation that put everything in the global namespace (i.e. didn't use the std namespace)
You might also need to use the -AA option when compiling. This tells the compiler to use the newer 2.x version of HP's STL library.
>aCC -AA temp.cpp
And it should always be
<iostream>
<iostream.h>
is from a pre-standard implementation of the language, though it is usually shipped so as to maintain backwards compatibility with older code.
Try with:
#include <iostream>
Instead of:
#include <iostream.h>
iostream.h is an old style header in which all functions are exposed in global namespace. naturally in such a case, using namespace std may not work since std namespace is probably not exposed by iostream.h header (in this compiler). As explained above, try with # include which is a new style C++ standard library header. (thanks Shailesh Kumar for the comment! included it in the answer).