I am trying to get a substring from a CString using C++. For that I am using strstr function. But it is not working at al
CString str = m_sectionDataList->GetNext(pos);
char* chToMatch = (char*)(LPCTSTR)str;
char *match = "=";
//char * sMatched = strstr(ch, match);
if (strstr(match, chToMatch) != NULL) {
MessageBox(NULL, str, L"Done", 1);
}
You are passing arguments in the incorrect order. strstr expects first argument to be scanned string, and second should be a match. Right now you are searching your target string in the one byte = template, which will most certainly fail.
Finally I've found it. Need to use a macro of C++ and you will found it converted.
CT2A ascii(str, CP_UTF8);
now you can just access it using ascii.m_psz and its buffer also.
Related
I've been looking around the internet for some solutions however they all convert it from a constant string. Here's a piece of code I took to convert strings to wchar_t without additional libraries. What I'm trying to do is, I want to change the background of my windows computer with my background. Now I can't assume that the folder that I downloaded is in C:\Downloads because some people change their downloads folder or maybe they moved the whole folder to another location. So in the first code, I'm trying to get the path of the .exe file.
string GetExePath() {
char buffer[MAX_PATH];
GetModuleFileNameA(NULL, buffer, MAX_PATH);
string::size_type pos = string(buffer).find_last_of("\\/");
return string(buffer).substr(0, pos + 1);//gets the first character in path up to the final backslash
}
Next I'm going to grab the picture that I want to make as my background in the same folder as the .exe file.
//error on the third parameter
int return_value = SystemParametersInfo(SPI_SETDESKWALLPAPER, 0, L(string)(GetExePath() + "\\picture.png"), SPIF_UPDATEINIFILE);
Error (active) E0040 expected an identifier
Error (active) E0020 identifier "L" is undefined
Error (active) E0254 type name is not allowed
Error (active) E0018 expected a ')'
After a while, I replaced the return type of the function and so it would return wchar_t*.
const wchar_t* GetExePath() {
char buffer[MAX_PATH];
GetModuleFileNameA(NULL, buffer, MAX_PATH);
string::size_type pos = string(buffer).find_last_of("\\/");
string path = string(buffer).substr(0, pos + 1);
path += "\\HandleCamWallpaperwithgradient.png";
cout << path << endl;
wstring wide;
for (int i = 0; i < path.length(); ++i){
wide += wchar_t(path[i]);
}
const wchar_t* result = wide.c_str();
return result;
}
However, the third parameter is showing an error saying
Error E0167 argument of type "const wchar_t *" is incompatible with parameter of type "PVOID"
So how can I fix it?
Edit: Someone thought that this was a duplicate and it isn't. How to convert string to wstring in C++ is NOT correlated with this question as the one who is asking on that thread is asking help for special characters.
Call the Unicode version GetModuleFileNameW() in the first place so you don't have to convert.
Also, never return a pointer to a string that is a local variable of a function (unless it is static)! Otherwise you will be returning a dangling pointer. Instead, return a std::wstring similar to your first version. You can use std::wstring directly as the buffer by using the "pointer-to-first-character" trick.
std::wstring GetExePath() {
std::wstring buffer(MAX_PATH, L'\0'); // reserve buffer
int len = GetModuleFileNameW(NULL, &buffer[0], buffer.size() );
buffer.resize(len); // resize to actual length
string::size_type pos = buffer.find_last_of(L"\\/");
return buffer.substr(0, pos + 1);//gets the first character in path up to the final backslash
}
The second error can be fixed like this:
std::wstring path = GetExePath() + L"picture.png";
int return_value = SystemParametersInfoW(SPI_SETDESKWALLPAPER, 0, &path[0], SPIF_UPDATEINIFILE);
The pvParam parameter of SystemParametersInfoW is a pointer to non-const data, so we have to use the "pointer-to-first-character" trick here again (to avoid ugly const_cast).
With C++17, this could be written as a one-liner:
int return_value = SystemParametersInfoW(SPI_SETDESKWALLPAPER, 0, (GetExePath() + L"picture.png").data(), SPIF_UPDATEINIFILE);
Other things to improve, left as an exercise:
Check for the error condition ERROR_INSUFFICIENT_BUFFER as described in the comments of GetModuleFileName() MSDN reference so you can support pathes longer than MAX_PATH.
I'm trying to understand why a segmentation fault (SIGSEGV) occurs during the execution of this piece of code. This error occurs when testing the condition specified in the while instruction, but it does not occur at the first iteration, but at the second iteration.
LPTSTR arrayStr[STR_COUNT];
LPTSTR inputStr;
LPTSTR str;
// calls a function from external library
// in order to set the inputStr string
set_input_str(param1, (char*)&inputStr, param3);
str = inputStr;
while( *str != '\0' )
{
if( debug )
printf("String[%d]: %s\n", i, (char*)str);
arrayStr[i] = str;
str = str + strlen((char*)str) + 1;
i++;
}
After reading this answer, I have done some research on the internet and found this article, so I tried to modify the above code, using this piece of code read in this article (see below). However, this change did not solve the problem.
for (LPTSTR pszz = pszzStart; *pszz; pszz += lstrlen(pszz) + 1) {
... do something with pszz ...
}
As assumed in this answer, it seems that the code expects double null terminated arrays of string. Therefore, I wonder how I could check the contents of the inputStr string, in order to check if it actually contains only one null terminator char.
NOTE: the number of characters in the string printed from printf instruction is twice the value returned by the lstrlen(str) function call at the first iteration.
OK, now that you've included the rest of the code it is clear that it is indeed meant to parse a set of consecutive strings. The problem is that you're mixing narrow and wide string types. All you need to do to fix it is change the variable definitions (and remove the casts):
char *arrayStr[STR_COUNT];
char *inputStr;
char *str;
// calls a function from external library
// in order to set the inputStr string
set_input_str(param1, &inputStr, param3);
str = inputStr;
while( *str != '\0' )
{
if( debug )
printf("String[%d]: %s\n", i, str);
arrayStr[i] = str;
str = str + strlen(str) + 1;
i++;
}
Specifically, the issue was occurring on this line:
while( *str != '\0' )
since you hadn't cast str to char * the comparison was looking for a wide nul rather than a narrow nul.
str = str + strlen(str) + 1;
You go out of bounds, change to
str = str + 1;
or simply:
str++;
Of course you are inconsistently using TSTR and strlen, the latter assuming TCHAR = char
In any case, strlen returns the length of the string, which is the number of characters it contains not including the nul character.
Your arithmetic is out by one but you know you have to add one to the length of the string when you allocate the buffer.
Here however you are starting at position 0 and adding the length which means you are at position len which is the length of the string. Now the string runs from offset 0 to offset len - 1 and offset len holds the null character. Offset len + 1 is out of bounds.
Sometimes you might get away with reading it, if there is extra padding, but it is undefined behaviour and here you got a segfault.
This looks to me like code that expects double null terminated arrays of strings. I suspect that you are passing a single null terminated string.
So you are using something like this:
const char* inputStr = "blah";
but the code expects two null terminators. Such as:
const char* inputStr = "blah\0";
or perhaps an input value with multiple strings:
const char* inputStr = "foo\0bar\0";
Note that these final two strings are indeed double null terminated. Although only one null terminator is written explicitly at the end of the string, the compiler adds another one implicitly.
Your question edit throws a new spanner in the works? The cast in
strlen((char*)str)
is massively dubious. If you need to cast then the cast must be wrong. One wonders what LPTSTR expands to for you. Presumably it expands to wchar_t* since you added that cast to make the code compile. And if so, then the cast does no good. You are lying to the compiler (str is not char*) and lying to the compiler never ends well.
The reason for the segmentation fault is already given by Alter's answer. However, I'd like to add that the usual style of parsing a C-style string is more elegant and less verbose
while (char ch = *str++)
{
// other instructions
// ...
}
The scope of ch is only within in the body of the loop.
Aside: Either tag the question as C or C++ but not both, they're different languages.
I encountered a problem during writting my code. I use a function which take as an argument object which type is LPCSTR. The object declaration looks like shown below:
LPCTSTR lpFileName;
Firstly, I used defined variable, which was futher assign to lpFileName like this:
#define COM_NR L"COM3"
lpFileName = COM_NR
Using this manner, I could easily pass lpFileName argument to the function. Anyway, i had to changed the way of defining my port number. Currently i read text from *.txt file and save it as string variable e.g "COM3" or "COM10". The main problem is to convert string to LPCSTR properly. I found good solution but finally it doesn't seem working properly. My code looks like this:
string temp;
\\code that fill temp\\
wstring ws;
ws.assign(temp.begin(),temp.end());
I thought that conversion went correctly, maybe it did and I don't get it because when i print few things it makes me to wonder why it doesn't work as i want:
cout temp_cstr(): COM3
cout LCOM3: 0x40e586
cout ws.c_str(): 0x8b49b2c
Why LCOM3 and ws.c_str() doesn't contain the same? When i pass lpFileName = ws.c_str() to my function, it works uncorretly. On the other hand, passing lpFileName = L"COM3" gives success.
I code using cpp, and IDE is QtCreator
Eventually, I managed with the pitfall using conversion-function s2ws() and doing few operations. I place my soultion here for people who will have similar troubles with converting string. In my first post i wrote that i needed to convert string to LPCTSTR and finally it turned out that argument in my function is not, LPCTSTR but LPCWSTR that is const wchar_t*.
So, soulution:
string = "COM3";
wstring stemp;
LPCWSTR result_port;
stemp = s2ws(port_nr);
result_port = stemp.c_str(); // now passing result_port to my function i am getting success
declaration of s2ws:
wstring s2ws(const std::string& s)
{
int len;
int slength = (int)s.length() + 1;
len = MultiByteToWideChar(CP_ACP, 0, s.c_str(), slength, 0, 0);
wchar_t* buf = new wchar_t[len];
MultiByteToWideChar(CP_ACP, 0, s.c_str(), slength, buf, len);
std::wstring r(buf);
delete[] buf;
return r;
}
Try to use wostringstream:
string temp;
\\code that fill temp\\
wostringstream ost;
ost << temp.c_str();
wstring ws = ost.str();
I have struggled with this for quite a while. After quite a bit of digging I found this works the best; you could try this.
std::string t = "xyz";
CA2T wt (t.c_str());
We have StringCchCat function in Win32Api,
Concatenates one string to another string. The size of the destination
buffer is provided to the function to ensure that StringCchCat does
not write past the end of this buffer.
Ok so ..
StringCchCat(dirWPath, MAX_PATH, TEXT("\\*"));
I ll get : dirWPath + "\\*"
I look for get a :"\\*" + dirWPath
Anyone have a solution ?
std::string first = dirWPath, second = "\\*";
std::string result = second + first;
You can just pass the wildcard first:
char str1[MAX_PATH] = "\\*";
StringCchCat(str1, MAX_PATH, dirWPath);
I need to format a string to be double null-terminated string in order to use SHFileOperation.
Interesting part is i found one of the following working, but not both:
// Example 1
CString szDir(_T("D:\\Test"));
szDir = szDir + _T('\0') + _T('\0');
// Example 2
CString szDir(_T("D:\\Test"));
szDir = szDir + _T("\0\0");
//Delete folder
SHFILEOPSTRUCT fileop;
fileop.hwnd = NULL; // no status display
fileop.wFunc = FO_DELETE; // delete operation
fileop.pFrom = szDir; // source file name as double null terminated string
fileop.pTo = NULL; // no destination needed
fileop.fFlags = FOF_NOCONFIRMATION|FOF_SILENT; // do not prompt the user
fileop.fAnyOperationsAborted = FALSE;
fileop.lpszProgressTitle = NULL;
fileop.hNameMappings = NULL;
int ret = SHFileOperation(&fileop);
Does anyone has idea on this?
Is there other way to append double-terminated string?
The CString class itself has no problem with a string containing a null character. The problem comes with putting null characters into the string in the first place. The first example works because it is appending a single character, not a string - it accepts the character as is without checking to see if it's null. The second example tries appending a typical C string, which by definition ends at the first null character - you're effectively appending an empty string.
You cannot use CString for this purpose. You will need to use your own char[] buffer:
char buf[100]; // or large enough
strcpy(buf, "string to use");
memcpy(buf + strlen(buf), "\0\0", 2);
Although you could do this by only copying one more NUL byte after the existing NUL terminator, I would prefer to copy two so that the source code more accurately reflects the intent of the programmer.