I have this code:
#include <array>
int main(int, char **argv)
{
std::array<int, 3> a = {1,2,3};
}
This compiles fine (-std=c++11) , but if you include -Wall it gives this warning that I don't understand:
clang_pp_error.cpp:5:28: warning: suggest braces around initialization of subobject [-Wmissing-braces]
std::array<int, 3> a = {1,2,3};
^~~~~
{ }
This should be a bug: https://llvm.org/bugs/show_bug.cgi?id=21629.
See also Is it wise to ignore gcc/clang's "-Wmissing-braces" warning?.
Use std::array<int, 3> a = {{1,2,3}}; instead.
See
Why wasn't a double curly braces syntax preferred for constructors taking a std::initializer_list
Related
This question already has answers here:
Format specifiers for uint8_t, uint16_t, ...?
(7 answers)
Closed 3 years ago.
My test code:
#include <cstdint>
#include <cstdio>
int main() {
const constexpr uint8_t x = 64;
printf("%u", x);
}
Here is how I compiled with GCC 8.2:
g++ -Wall test_format.cpp -o test_format -O3 -std=c++17 -Wformat-signedness
And here is GCC's output:
test_format.cpp: In function ‘int main()’:
test_format.cpp:6:9: warning: format ‘%u’ expects argument of type ‘unsigned int’, but argument 2 has type ‘int’ [-Wformat=]
printf("%u", x);
^~~~
Tho, if I try to print an uint32_t, it has no error/warning.
I wonder why GCC expects uint8_t to be signed int.
Thanks.
Default argument promotions are applied to operands of a variadic function. Under these, an expression of type unsigned char is promoted to int.
In C and C++ types narrower than int are always promoted to int. See Why must a short be converted to an int before arithmetic operations in C and C++?
And inside variadic functions default promotion also applies, which means you can't pass types narrower than int to vararg functions. So uint8_t must be printed with %d, not %u. But anyway you're printing it the wrong way. The correct way is to use PRIu8
printf("%" PRIu8 "\n", x);
Format specifiers for uint8_t, uint16_t, ...?
printing the uint8_t
Why is the format specifier for uint8_t and uint16_t the same (%u)?
How do I print uint32_t and uint16_t variables value?
To print a uint8_t variable with printf(), you should do something like the following:
#include <cinttypes>
#include <cstdio>
int print_u8(std::uint8_t x) {
return std::printf("%" PRIu8 "\n", x);
}
The <cinttypes> header includes printf and scanf format specifiers for all the <cstdint> types (and explicitly includes that header) that should be used for maximum portability.
I am new to coding and I keep getting stuck in the first few lines of code and I cannot figure out why. This is what I have so far:
#include <stdio.h>
#include <cs50.h>
int main(void);
int n;
{
printf("Minute: ");
int n = get_int();
}
I am getting this message when I try to compile the code:
What did I do wrong?
You're trying to call the main function. You should only define it. It will be called when the program is executed (it is the "entry point").
To define it, remove the semicolon after
int main(void)
You can also remove that void keyword
Then move that line down, between
int n; and the { that comes after it
Additionally, you're declaring the n variable twice. After you fix the first error, the compiler will complain about this one. Remove one of the declarations then.
You should remove the semicolon after int main(void) and move the variable declaration for n within the braces. Here is the correct code below.
#include <stdio.h>
#include <cs50.h>
int main(void)
{
int n;
printf("Minute: ");
int n = get_int();
}
In my program I try to convert a int to a char[20];
I try to do this in the following way:
char str[20];
sprintf(str, "%d", timer);
in which timer is the int.
But when I build this code, I get the following warnings.
Type implicit declaration of function 'sprintf' [-Wimplicit-function-declaration]
incompatible implicit declaration of built-in function 'sprintf' [enabled by default]
what does that mean?
note:( I have included string.h and stdlib.h).
great, I added stdio.h to my code and now the warnings disappeared only to give me a even harder error.
undefined reference to `_sbrk'
You have to #include <stdio.h> to use sprintf()
you want to make sure you also add reference to stdio.h see this ref
You probably need to put sprintf(str, "%d", timer) inside a function (not on the global part of the source code).
Something like:
#include <stdlib.h>
char str[20];
// SPOT #1
int f() {
sprintf(str, "%d", timer); // this won't work if placed on SPOT #1
}
When I compile this code in Visual C++, I got the below error. Can help me solve this issue..
DWORD nBufferLength = MAX_PATH;
char szCurrentDirectory[MAX_PATH + 1];
GetCurrentDirectory(nBufferLength, szCurrentDirectory);
szCurrentDirectory[MAX_PATH +1 ] = '\0';
Error message:
Error 5 error C2664: 'GetCurrentDirectoryW' : cannot convert parameter 2 from 'char [261]' to 'LPWSTR' c:\car.cpp
Your program is configured to be compiled as unicode. Thats why GetCurrentDirectory is GetCurrentDirectoryW, which expects a LPWSTR (wchar_t*).
GetCurrentDirectoryW expects a wchar_t instead of char array. You can do this using TCHAR, which - like GetCurrentDirectory - depends on the unicode setting and always represents the appropriate character type.
Don't forget to prepend your '\0' with an L in order to make the char literal unicode, too!
It seems you have define UNICODE, _UNICODE compiler flags. In that case, you need to change the type of szCurrentDirectory from char to TCHAR.
Headers:
#include <iostream>
#include <fstream>
#include <direct.h>
#include <string.h>
#include <windows.h> //not sure
Function to get current directory:
std::string getCurrentDirectoryOnWindows()
{
const unsigned long maxDir = 260;
wchar_t currentDir[maxDir];
GetCurrentDirectory(maxDir, currentDir);
std::wstring ws(currentDir);
std::string current_dir(ws.begin(), ws.end());
return std::string(current_dir);
}
To call function:
std::string path = getCurrentDirectoryOnWindows(); //Output like: C:\Users\NameUser\Documents\Programming\MFC Program 5
To make dir (Folder) in current directory:
std::string FolderName = "NewFolder";
std::string Dir1 = getCurrentDirectoryOnWindows() + "\\" + FolderName;
_mkdir(Dir1.c_str());
This works for me in MFC C++.
I'm trying to compile VC6 project with VC10...
I obtain an error C2678 with set_intersection: I wrote some example to understand. Can anybody explain how to compile this snippets ?
#include <vector>
#include <algorithm>
#include <iostream>
#include <set>
#include <string>
int main( )
{
using namespace std;
typedef set<string> MyType;
MyType in1, in2, out;
MyType::iterator out_iter(out.begin());
set_intersection(in1.begin(),in1.end(), in2.begin(), in2.end(), out_iter);
}
The output :
c:\program files\microsoft visual\studio 10.0\vc\include\algorithm(4494): error C2678: '=' binary : no operator defined which takes a left-hand operand of type 'const std::basic_string<_Elem,_Traits,_Ax>' (or there is no acceptable conversion)
If I use a std::vector instead of std::set the compilation succeeded.
acceptable)
Try
set_intersection(in1.begin(),in1.end(), in2.begin(), in2.end(), inserter(out, out.begin()) );
This is because set_intersection wants to write to the output iterator, which causes the output container to grow in size. However this couldn't be done with just an iterator alone (it could be used to overwrite existing elements but not grow in size)
Edit: fixed the typo. Use inserter for adding to a set. A back_inserter only works for vectors and such.
Edit 2: fixed another typo. STL inserter requires a second argument which is a hint iterator to the likely insert position. Thanks chepseskaf.