Even though I've included the < ranges > header in my code the compiler doesn't register it and causes errors when I try to run the code.
#include <iostream>
#include <iomanip>
#include <numeric>
#include <algorithm>
#include <ranges>
using namespace std;
int main() {
for (int i : views::iota(1, 11)) //this is the function supposedly included in the <ranges> library
cout << i << endl;
return 0;
};
When I runstd::cout << __cplusplus I get the output 202002 which means that in theory VS Code and the compiler are successfully reading that it's C++20. My compiler version is Apple clang version 13.1.6. I'm not sure how to change the language standard, but since I'm getting the C++20 output then it should have the right standard?
I've tried online compilers and the code runs just fine. Any idea on something else I can try?
Related
my question is pretty simple but I can't seem to find it out.
I want to know what libary to include when using stoi. I was using atoi and it works fine with
#include <iostream>
#include <string>
#include <stdlib.h>
using namespace std;
but I get "stoi not declared" when I run with stoi. Thanks
You need to #include <string> and use a compiler that understands C++11. Minimal example:
#include <string>
#include <cassert>
int main()
{
std::string example = "1234";
int i = std::stoi(example);
assert(i == 1234);
return 0;
}
Compile, for example, with g++ -std=c++11.
I've been puzzled by this for a while. To test this out, I made a simple program that just creates a std::string variable and prints it out to the screen. However, it doesn't include <string.h>.
#include <iostream>
using namespace std;
int main()
{
string name = "Test";
cout << name << endl;
return 0;
}
What confuses me is that this program compiles and runs perfectly. Right now I'm using the clang compiler that came with the XCode Developer Tools. Is this intended behavior? I hope this question isn't too ridiculous since I just started learning C++.
The reason you do not need to include the #include <string.h> header file is because when you include the #include <iostream> header file it includes std::string.
However, do not rely on it. What may work on your compiler may not work on another. Always include the proper header files.
To edit your example this is how you should use it:
#include <iostream>
#include <string>
int main()
{
std::string name = "Test";
std::cout << name << std::endl;
return 0;
}
Also note: why you should not use using namespace std;.
Why does my program compile successfully if I don't include <string.h>?
Because you don't use any definition / declaration from <string.h>.
program compiles and runs perfectly ... Is this intended behavior?
It is incidental behaviour.
There are no guarantees that one standard header wouldn't include other standard headers. It just so happens that <iostream> included <string> in this particular version of the standard library. Since there is no guarantee for this, it would be a mistake to rely on such transitive inclusion.
I've been trying to learn C++ over the past couple of days, and ran into a problem when I was trying to use the getline() and stoi() methods in some practice code:
#include <string>
#include <fstream>
#include "stdafx.h"
#include <iostream>
using namespace std;
int main()
{
string numberGuessed;
int intNumberGuessed = 0;
do {
cout << "Guess a number between 1 and 10";
getline(cin, numberGuessed);
intNumberGuessed = (stoi(numberGuessed));
cout << intNumberGuessed << "\n";
} while (intNumberGuessed != 4);
cout << "You win\n";
return 0;
}`
When I tried to build this code in VS 2015, the console could not identify getline or stoi as if I hadn't added #include statements for string and fstream. Is there something wrong with my code or is it something to do with VS?
It's something to do with VS.
Since you have
#include "stdafx.h"
I'm guessing you have precompiled headers turned on, and "stdafx.h" is the precompiled header. (That's the default name in VS)
With precompiled headers turned on, anything before the include statement for the precompiled header is ignored.
Either make sure #include "stdafx.h" is the very first thing in the file (except for comments), or turn off precompiled headers.
I have been trying to debug this problem for a while and quite honestly, I just can't see what I'm doing wrong.
Why is there a syntax error?
#include <iostream>;
#include <time.h>;
#include <stdio.h>;
#include <stdlib.h>;
using namespace std;
class Problem3 {
public:
bool isPrime(long double num) {
srand(time(NULL));
return 0;
}
};
The error I'm getting is,
"Function 'srand' could not be resolved."
I'm well aware now that I don't need the semi-colons after 'include' statements
I'm using Eclipse CDT along with MinGW as my compiler
How I resolved the problem:
It had to do with the MinGW compiler I was using. Switching over to Visual Studio solved the problem.
; at the end of the #include directives are the problem in your code. #include directives don't need (wrong to place indeed) semicolons at the end unlike C++ statements.
[Warning] extra tokens at end of #include directive [enabled by default]
It seems any character after > in the directive causes this error/warning.
#include<iostream>a //error
Change to this:
#include <iostream>
#include <time.h>
#include <stdio.h>
#include <stdlib.h>
using namespace std;
class Problem3 {
public:
bool isPrime(long double num) {
srand(time(NULL));
return 0;
}
};
int main(){
cout<<"Hello Main";
}
EDIT:
Regarding the linker issue:
One suggestion is C++ expects types to be explicitly casted between types (more than C). So, use a cast to convert time_t which is returned by the time to unsigned int which is the input parameter type of srand. (And of course this might not be the problem with linker error)
Instead of using stdlib.h, try using <cstdlib>, try if it helps. Because it uses namespace.
Apart from that, I have seen this snippet here. Use that pattern if it helps.
#include <cstdlib>
#include <iostream>
#include <ctime>
using namespace std;
int main()
{
srand(time(0)); //use current time as seed for random generator
int random_variable = rand();
cout << "Random value on [0 " << RAND_MAX << "]: "
<< random_variable << '\n';
}
there is already question in SO check if that helps Eclipse Method could not be resolved in a simple program C++
Never use time() to initialize srand()..
EDIT:
Now it seems many people got this kind of problem. I found a question How do I fix Eclipse CDT Error “Function 'isdigit' could not be resolved. He is facing the same problem. The asker suggested a work around to this in his question edit.
Quoted from that question:
I now believe this to be a Code Analysis problem. A better solution is
to edit the Code Analysis options to make "Function could not be
resolved" be a warning instead of an error. That way you can see the
warnings in Problems view, but continue to work. If the function is
REALLY missing, the compiler will tell you! I also have a new theory,
that the problem is with the Code Analyzer following symlinks, because
all of the "missing" functions are in symlinked include files. Would
love any input on this theory.
Hope that points to solve the problem.
; should not be there after #include.
#include <iostream>
#include <time.h>
#include <stdio.h>
#include <stdlib.h>
#include files shoule not end with ;
Here is some code that used to work with my code, but is having a problem now:
#include <iostream>
#include <fstream>
#include <sstream>
#include <cstring>
using namespace std;
int main()
{
stringstream out;
out << 100;
cout << out.str();
}
I get just blank output. I just changed to snow leopard with Xcode 3.2.
Get this exact same issue under the same conditions Snow Leopard 64-Bit XCode 3.2 Base SDK 10.6 and the switch to Base SDK 10.5 resolves it.
Apparently it's a SDK 10.6 issue.
and the correct workaround is to remove the preprocessor macros:
_GLIBCXX_DEBUG=1
_GLIBCXX_DEBUG_PEDANTIC=1
From the preprocessor settings (or else fall back to SDK 10.5 as above).
Apple Discussion Link
it works for me. if there's a problem, it should be your gcc's.
btw, maybe you have to add fflush(stdout); after the cout << sometime the problem is stdout buffer
#include <iostream>
#include <fstream>
#include <sstream>
#include <cstring>
using namespace std;
int main()
{
stringstream out;
out << 100;
cout << out.str();
fflush(stdout);
}
Another idea is that you have a .o file left over from before you upgraded that's somehow messing things up. Mixing .o files from two different versions of the C++ compiler can cause all kinds of strange problems. I also do not discount the header file issue as well, though sstream should be including string.
Shouldn't you add the end of string before converting to string?
cout << out.str() << sdt::ends;