I am getting a text value from text box and need to pass this to a _mkdir function which takes char*.
So I have:
_mkdir(this->txt_path->Text);
How do I convert this, I am using VS 2008 C++ and have .Net env.
I have looked at other online material which hasn't helped :(
Thanks,
Bruce
Well, like most C API's this one is probably not const correct. You could try to pass in Text.c_str() and see what happens.
If it really does need to modify the string though then first of all, find another function to use, this is a very unsafe one. Second of all, you can use it by doing this:
std::vector<char> buf(Text.begin(), Text.end());
buf.push_back(0);
_mkdir(&buf[0]);
Related
I've tried out using memcpy() method to strings but was getting a "no matching function call" although it works perfectly when I use an array of char[].
Can someone explain why?
www.cplusplus.com/reference/cstring/memcpy/
std::string is an object, not a contiguous array of bytes (which is what memcpy expects). std::string is not char*; std::string contains char* (somewhere really deep).
Although you can pull out the std::string inner byte array by using &str[0] (see note), I strongly encourage you not to. Almost anything you need to do already is implemented as a std::string method. Including appending, subtracting, transforming and anything that makes sense with a text object.
So yes, you can do something as stupid as:
std::string str (100,0);
memcpy(&str[0],"hello world", 11);
but you shouldn't.
Even if you do need memcpy behaviuor, try to use std::copy instead.
Note: this is often done with C functions that expects some buffer, while the developer wants to maintain a RAII style in his code. So he or she produces std::string object but passes it as C string. But if you do clean C++ code you don't need to.
Because there's no matching function call. You're trying to use C library functions with C++ types.
I am aware that in Pro*C is possible to pass to a procedure either a host variable or a String literal:
dbms_pipe.purge(:pipe_name);
dbms_pipe.purge('pipe_name');
Is it possible to pass a method return to a Pro*C procedure? The following call don't work:
dbms_pipe.purge(pipe_name.c_str());
Late answer, but still:
First of all, Pro*C is quite dumb. It becomes even more dumb when switching from C to C++-Mode.
Your second example does not challenge Pro*C at all, because the string constant is just part of your sql-statement.
Your first example is just what it can do. You cannot access members of structs (But you can read in whole structs), call functions or whatever. The only way to deal with this is first to copy the result of the function call into a host-variable and then pass that to Pro*C. To find the Manual, try google search for "oracle pro*c developer guide". If you read it carefully, you will understand what you can do and what not...
I have ran the code analyzer in visual studio on a large code base and i got about a billion of this error:
warning C6284: Object passed as parameter '3' when string is required in call to 'fprintf'
According to http://msdn.microsoft.com/en-us/library/ta308ywy.aspx "This defect might produce incorrect output or crashes." My colleague however states that we can just ignore all these errors without any problems. So one of my questions is do we need to do anything about this or can we just leave it as is?
If these errors need to be solved what is the nicest approach to solve it?
Would it work to do like this:
static_cast<const char*>(someCString)
Is there a better or more correct approach for this?
The following lines generate this warning:
CString str;
fprintf(pFile, "text %s", str);
I'm assuming that you're passing a Microsoft "CString" object to a printf()-family function where the corresponding format specifier is %s. If I'm right, then your answer is here: How can CString be passed to format string %s? (in short, your code is OK).
It seems that originally an implementation detail allowed CString to be passed directly to printf(), and later it was made part of the contract. So you're good to go as far as your program being correct, but if you want to avoid the static analysis warning, you may indeed need to use the static_cast to a char pointer. I'm not sure it's worth it here...maybe there's some other way to make these tools place nice together, since they're all from Microsoft.
Following the MSDN suggestions in C6284, you may cast the warnings away. Using C++ casts will be the most maintainable option to do this. Your example above would change to
fprintf(pFile, "text %s", static_cast<const TCHAR*>(str));
or, just another spelling of the same, to
fprintf(pFile, "text %s", static_cast<LPCTSTR>(str));
The most convincing option (100% cast-free, see Edits section) is
fprintf(pFile, "text %s", str.GetString());
Of course, following any of these change patterns will be a first porting step, and if nothing indicates a need for it, this may be harmful (not only for your team atmosphere).
Edits: (according to the comment of xMRi)
1) I added const because the argument is read-only for fprintf
2) notes to the cast-free solution CSimpleStringT::GetString: the CSimpleStringT class template is used for the definition of CStringT which again is used to typedef the class CString used in the original question
3) reworked answer to remove noise.
4) reduced the intro about the casting option
Technically speaking it is ok because the c-string is stored in such a way in CString that you can use it as stated but it is not good rely on how CString is implemented to do a shortcut. printf is a C-runtime function and knows nothing about C++ objects but here one is relying on an that the string is stored first in the CString - an implementation detail.
If I recall correctly originally CString could not be used that way and one had to cast the CString to a c-string to print it out but in later versions MS changed the implementation to allow for it to be treated as a c-string.
Another breaking issue is UNICODE, it will definitely not work if you one day decide to compile the program with UNICODE character set since even if you changed all string formatters to %ld, embedded 0s will sometimes prevent the string from being printed.
The actual problem is rather why are you using printf instead of C++ to print/write files?
I have some code which is relatively big, but there is one part of it which uses something called CString (http://msdn.microsoft.com/en-us/library/aa300688%28v=vs.60%29.aspx) . Right now I am using the mingw compiler on eclipse and it doesnt seem to recognize it which makes sense. But I need to use the other part of the code. I know I can replace the CString with a const char * but there are several function like append which the code uses which are not defined. I was wondering whats the best way to port this code? Also there are other stdafx.h dependencies also like _T(). Whats the best approach I should take now?
There is a CString replacement over on CodeProject. I just googled for "CString alternative". I haven't looked at it but it should be easier to use that instead of std::string.
I need to get the protocol version of an application, and I don't know too much about the inner workings of detouring. I usually use a detour class written by a friend of mine (Not windows detour, as this works on win/linux) but im wondering if anyone can give me some insight on how to retrieve the value of a global pointer? I found a function which uses it, but the class I use only allows for you to rewrite functions, not access individual lines. Here is what the assembly looks like from IDA...
I need to get the value of "gpszVersionString_ptr"
http://www.ampaste.net/m57f13aba
Edit
Sorry, it lost formatting so i had to ampaste it.
if it's already a compiled binary. How about extracting the string using string pattern match?
For example you can read in the file char by char and search for the pattern:
Protocol version %i\nExe version %s
(%s)