When compiling the below code, it gives me a warning, namely
deprecated conversion from string constant to 'char*'.
In what ways is it possible to remove the message (without explicitly suppressing the warning)?
I tried casting with (const char*), but to no avail.
#include <windows.h>
int main() {
typedef int * (*MyDownloadToUrl)(void*, char*, char*, DWORD, void*);
HINSTANCE LibHnd = LoadLibrary("Urlmon.dll");
MyDownloadToUrl MyDownloadFunction = (MyDownloadToUrl)GetProcAddress(LibHnd,"URLDownloadToFileA");
MyDownloadFunction(0, "http://MyWebsite.com", "Webpage.htm", 0, NULL);
}
You need to const_cast<char*>("my string literal") to get rid of the warning. In C++03 implicit conversion from a string literal (which is a const char*) to char* is deprecated. In C++11 such an implicit conversion is an error.
In this case though, URLDownloadToFile takes arguments of type LPCTSTR, which is defined as either const wchar_t* or const char* depending on the UNICODE prepossessor directive.
Related
I have overloaded function
int put_message(int level, int sys_log_level, const char * inp_message);
int put_message(int level, int sys_log_level, const std::string &inp_message);
and call this function
put_message(0, LOG_ERR, "clock_gettime error");
Code is compiled and works
but Eclipse CDT Code analyzer says
Invalid arguments '
Candidates are:
int put_message(int, int, const char *)
int put_message(int, int, const ? &)
'
How can I fix this the error?
Update:
After modifying LOG_ERR to int(LOG_ERR) error disappears.
I have not add the in the header.
Adding solves the problem.
you are missing #include <string> or something related to string class
You need to cast the string to the correct type, the compiler treats "some string" as char[] so you need to cast it to const char*
Try with
put_message(0, LOG_ERR, (const char*)"clock_gettime error");
I need LPOLESTR (Long Pointer OLE String) as an argument to a simple function call.
According to The Complete Guide to C++ Strings, Part II - String Wrapper Classes
OLECHAR is a Unicode character (wchar_t)
LPOLESTR is a string of OLECHAR (OLECHAR*)
So I should be able to do this:
int demo(LPOLESTR ptName) {
return 1;
}
int main(){
demo(L"Visible");
}
But I'm getting a compile error:
(const wchar_t[8])L"Visible"
argument of type "const wchar_t *" is incompatible with parameter of type "LPOLESTR"
or maybe I'll try a variable:
LPOLESTR lVis = L"Visible";
But I get this compiler error:
(const wchar_t[8])L"Visible"
a value of type "const wchar_t *" cannot be used to initialize an entity of type "LPOLESTR"
I have #include <string> at the top.
This seems like it should be a simple thing but I've been Googling all morning and can't find the answer. How do I create a variable or constant of type LPOLESTR in C++?
The problem you have is that LPOLESTR is a typedef for wchar_t*.
A compiler will not allow you to convert a const wchar_t* to a wchar_t* without an explicit const_cast.
Writing, using an alternative type LPCOLESTR:
LPCOLESTR lVis = L"Visible";
will fix the immediate compilation error as would the more Windows-like and probably preferred by Windows programmers.
Using a const_cast is, in general, not advisable but you will get away with it if the function documentation states that it does not attempt to modify the data passed to it.
When I compile in Visual Studio 2022 and by using standard C++20, I get similar error messages.
*Error (active) E0167 argument of type "const wchar_t *" is incompatible with parameter of type "LPOLESTR"*
I needed to pass through the compilation by avoiding "strict const-qualification" conformance by using compiler option "/Zc:strictStrings-"
Project Properties | C/C++ | Command Line -- add the compiler option.
I am trying to create a user defined literal but get an error message when using it.
GCC says
unable to find numeric literal operator ‘operator""_uint’
while clang tells me
error: no matching literal operator for call to 'operator""_uint' with argument of type 'unsigned long long' or 'const char *', and no matching literal operator template
I reduced the code to following MCVE:
#include <cinttypes>
unsigned int operator"" _uint(char const *, std::size_t) { return 0; }
int main() {
return 1_uint;
}
Which gives the mentioned error as you can see on ideone.
As you can read in detail on cppreference.com there is a multitude of different versions for literal operators.
The one in the OP is used exclusively for string literals and won't be available for integers. Instead the "fallback" version for integers which expects only a const char* without a second std::size_t parameter:
#include <cinttypes>
unsigned int operator"" _uint(char const *) { return 0; }
int main() {
return 1_uint;
}
Which works on ideone.
im developin QT application, and i need to include pure C code. When i compile this code in code::blocks it was successful, maybe one warning, but when i try to compile it in QT creator, i get these 4 errors.
cannot convert 'char*' to 'WCHAR*' for argument '1' to 'UINT GetSystemDirectoryW(WCHAR*, UINT)'
cannot convert 'char*' to 'const WCHAR*' for argument '1' to 'HINSTANCE__* LoadLibraryW(const WCHAR*)'
cannot convert 'char*' to 'WCHAR*' for argument '1' to 'BOOL
cannot convert 'const char*' to 'const WCHAR*' for argument '2' to 'LONG RegQueryValueExW(HKEY__*, const WCHAR*, DWORD*, DWORD*, BYTE*, DWORD*)'
and the code is here>
char systemDirectory[MAX_PATH];
GetSystemDirectory(systemDirectory, MAX_PATH); //first error
char kbdLayoutFilePath[MAX_PATH];
kbdLibrary = LoadLibrary(kbdLayoutFilePath); //second error
char kbdName[KL_NAMELENGTH];
GetKeyboardLayoutName(kbdName); //third error
if(RegQueryValueEx(hKey, "Layout File", NULL, &varType, layoutFile, &bufferSize) != ERROR_SUCCESS) //fourth error
i also use snprintf function, so i cant just change the type from char to WCHAR, because then it wont compile the snprintf
snprintf(kbdKeyPath, 51 + KL_NAMELENGTH,
"SYSTEM\\CurrentControlSet\\Control\\Keyboard Layouts\\%s", kbdName);
So do you have any ideas how to fix it ? first i tried change type from char to WCHAR, but then the snprintf didnt work, so i tried to use swprinf, but with no success, since strangely it didnt find this function
int swprintf(wchar_t *wcs, size_t maxlen,
const wchar_t *format, ...);
but just this
int swprintf(wchar_t *wcs,
const wchar_t *format, ...);
so what are my option ? How to compile pure C code in c++ environment without any errors... or how to make the right type conversion.
You are compiling in Unicode mode. You could set your compile to multi-byte strings. The problem that is happening is those windows API functions are macros that check whether you are building Unicode or not and then call either the W or A version of the function (in your code there, the GetSystemDirectory is actually calling GetSystemDirectoryW. So, you can either change your compile to multi-byte strings....or you could explicitly change your api calls to call the A version (i.e. GetSystemDirectoryA)
You are compiling your project with the UNICODE or _UNICODE define. Check your project settings and remove the define if necessary. To remove the define, you might need to disable unicode support for the whole project.
Change over from char to WCHAR and then to solve your swprintf problem just do this
#define swprintf _snwprintf
On Windows, the prototype of swprintf is
int swprintf( wchar_t *buffer,const wchar_t *format [,argument] ... );
But the ISO C Standard requires the following prototype for swprintf
int swprintf (wchar_t *, size_t, const wchar_t *, ...);
For this very reason, on Windows, _snwprintf is provided.
Read this for more details
http://msdn.microsoft.com/en-us/library/ybk95axf(v=vs.71).aspx
I am trying to compile some code that was given to me that I'm told compiles fine. Perhaps on a different compiler. I am using VS2010 and I have the following line:
char *dot = strrchr(filename, '.');
This causes the compiler error:
"error C2440: 'initializing': cannot convert from 'const char *' to
'char *'
How come? And how do I fix it?
The error message is pretty clear. strrchr returns a const char*. So you need:
const char *dot = strrchr(filename, '.');
If you really need a char*, you can use strcpy for conversion.
C++ has saner versions of strchr and strrchr than C thanks to overloading, so say:
const char * dot = strrchr(filename, '.');
In C, which has no overloading, you only have a single function char * strrchar(const char *, const char *), and it's up to you to decide whether the result is constant or mutable, depending on which type of pointer to feed into the function. C has many such type-unsafe functions.