So I have the following code which doesn't work. I couldn't figure it out how to do it.
std::string str("Q850?51'18.23"");
First problem I face is " (quotation mark). I cannot save it as a string because at the end of the string I have two " characters and C++ doesn't let me save the whole string.
Second I want to split the string and save it in different variables.
E.g.;
double i = 850;
double j = 51;
double k = 18.23;
You will need to escape the quotation mark you require in the string;
std::string str("Q850?51'18.23\"");
// ^ escape the quote here
The cppreference site has a list of these escape sequences.
Alternatively you are use a raw string literal;
std::string str = R"(Q850?51'18.23")";
The second part of the problem is dependent on the format and predictability of the data;
If it is fixed width, a simple index and be used to extract the numbers and convert to the double you require.
If it is delimited with the characters above, you can consume the string to each of the delimiters extracting the numbers in-between them (you should be able to find suitable libraries to assist with this).
If it is some further unknown composition, you may be limited to consuming the string one character at a time and extracting the numerical values between the non-numerical values.
You need to escape your quote mark:
std::string str("Q850?51'18.23\"");
// ^
You need to escape your quote mark
Add a backslash before "
std::string str("Q850?51'18.23\"");
Related
I have a QString like this:
QString fileData = "SOFT_PACKAGES.ABC=MY_DISPLAY_OS:MY-Display-OS.2022-3.10.25.10086-1.myApplication"
What I need to do is to create substrings as follow:
SoftwareName = MY_DISPLAY_OS //text after ':'
Version = 10.25.10086-1
Release = 2022-3
I tried using QString QString::sliced(qsizetype pos, qsizetype n) const but didn't worked as I'm using 5.9 and this is supported on 6.0.
QString fileData = "SOFT_PACKAGES.ABC=MY_DISPLAY_OS:MY-Display-OS.2022-3.10.25.10086-1.myApplication";
QString SoftwareName = fileData.sliced(fileData.lastIndexOf(':'), fileData.indexOf('.'));
Please help me to code this in Qt.
Use QString::split 3 times:
Split by QLatin1Char('=') to two parts:
SOFT_PACKAGES.ABC
MY_DISPLAY_OS:MY-Display-OS.2022-3.10.25.10086-1.myApplication
Next, split 2nd part by QLatin1Char(':'), probably again to just 2 parts if there can never be more than 2 parts, so the 2nd part can contain colons:
MY_DISPLAY_OS
MY-Display-OS.2022-3.10.25.10086-1.myApplication
Finally, split 2nd part of previous step by QLatin1Char('.'):
MY-Display-OS
2022-3
10
25
10086-1
myApplication
Now just assemble your required output strings from these parts. If exact number of parts is unknown, you can get Version = 10.25.10086-1 by removing two first elements and last element from the final list above, and then joining the rest by QLatin1Char('.'). If indexes are known and fixed, you can just use QStringLiteral("%1.%2.%3").arg(....
One way is using
QString::mid(int startIndex, int howManyChar);
so you probably want something like this:
QString fileData = "SOFT_PACKAGES.ABC=MY_DISPLAY_OS:MY-Display-OS.2022-3.10.25.10086-1.myApplication";
QString SoftwareName = fileData.mid(fileData.indexOf('.')+1, (fileData.lastIndexOf(':') - fileData.indexOf('.')-1));
To extract the other part you requested and if the number of '.' characters remains constant along all strings you want to check you can use the second argument IndexOf to find shift the starting location to skip known many occurences of '.', so for example
int StartIndex = 0;
int firstIndex = fileData.indexOf('.');
for (int i=0; i<=6; i++) {
StartIndex += fileData.indexOf('.', firstIndex+StartIndex);
}
int EndIndex = fileData.indexOf('.', StartIndex+8);
should give the right indices to be cut out with
QString SoftwareVersion = fileData.mid(StartIndex, EndIndex - StartIndex);
If the strings to be parsed stay less consistent in this way, try switching to regular expressions, they are the more flexible approach.
In my experience, using regular expressions for these types of tasks is generally simpler and more robust. You can do this with a regular expressions with the following:
// Create the regular expression.
// Using C++ raw string literal to reduce use of escape characters.
QRegularExpression re(R"(.+=([\w_]+):[\w-]+\.(\d+-\d+)\.(\d+\.\d+\.\d+-?\d+))");
// Match against your string
auto match = re.match("SOFT_PACKAGES.ABC=MY_DISPLAY_OS:MY-Display-OS.2022-3.10.25.10086-1.myApplication");
// Now extract the portions you are interested in
// match.captured(0) is always the full string that matched the entire expression
const auto softwareName = match.captured(1);
const auto version = match.captured(3);
const auto release = match.captured(2);
Of course for this to make sense, you have to understand regex, so here is my explanation of the regex used here:
.+=([\w_]+):[\w-]+\.(\d+-\d+)\.(\d+\.\d+\.\d+-?\d+)
.+=
get all characters up to and including the first equals sign
([\w_]+)
capture one or more word characters (alphanumeric characters) or underscores
:
a colon
[\w-]+\.
one or more alphanumeric or dash characters followed by a single period
(\d+-\d+)
capture one or more of digits followed by a dash followed by one or more digits
\.
a single period
(\d+\.\d+\.\d+-?\d*)
capture three sets of digits with periods in between, then an optional dash, and any number of digits (could be zero digits)
I think it is generally easier to make a regex that handles changes to the input - lets say version becomes 10.25.10087 - more easily than manually parsing things by index.
Regex is a powerful tool once you get used to it, but it can certainly seem daunting at first.
Example of this regex on regex101.com: https://regex101.com/r/dj3Z4U/1
so there's a text file where I have 1. languages, a 2. text of a number written in the said language, 3. the base of the number and 4. the number written in digits. Here's a sample:
francais deux mille quatre cents 10 2400
How I went about it:
struct Nomen{
char langue[21], nomNombre [31], baseC[3], nombreC[21];
int base, nombre;
};
and in the main:
if(myfile.is_open()){
{
while(getline(myfile, line))
{
strcpy(Linguo[i].langue, strtok((char *)line.c_str(), " "));
strcpy(Linguo[i].nomNombre, strtok(NULL, " "));
strcpy(Linguo[i].baseC, strtok(NULL, " "));
strcpy(Linguo[i].nombreC, strtok(NULL, "\n"));
i++;
}
Difficulty: I'm trying to put two whitespaces as a delimiter, but it seems that strtok() counts it as if there were only one whitespace. The fact there are spaces in the text number, etc. is messing up the tokenization. How should I go about it?
strtok treats any single character in the provided string as a delimiter. It does not treat the string itself as a single delimiter. So " " (two spaces) is the same as " " (one space).
strtok will also treat multiple delimiters together as a single delimiter. So the input "t1 t2" will be tokenized as two tokens, "t1" and "t2".
As mentioned in comments, strtok is also writes the NUL character into the input to create the token strings. So, it is an error to pass the result of string::c_str() as input to the function. The fact that you need to cast the constant string should have been enough to dissuade you from this approach.
If you want to treat a double space as a delimiter, you will have to scan the string and search for them yourself. Given you are using C APIs, you can consider strstr. However, in C++, you can use string::find.
Here's an algorithm to parse your string manually:
Given an input string input:
language is the substring from the start of input to the first SPC character.
From where language ends, skip over all whitespace, changing input to begin at the first non-whitespace character.
text is the substring from the start of input to the first double SPC sequence.
From where text ends, skip over all whitespace, changing input to begin at the first non-whitespace character.
Parse base, and parse number.
I could have a string like:
During this time , Bond meets a stunning IRS agent , whom he seduces .
I need to remove the extra spaces before the comma and before the period in my whole string. I tried throwing this into a char vector and only not push_back if the current char was " " and the following char was a "." or "," but it did not work. I know there is a simple way to do it maybe using trim(), find(), or erase() or some kind of regex but I am not the most familiar with regex.
A solution could be (using regex library):
std::string fix_string(const std::string& str) {
static const std::regex rgx_pattern("\\s+(?=[\\.,])");
std::string rtn;
rtn.reserve(str.size());
std::regex_replace(std::back_insert_iterator<std::string>(rtn),
str.cbegin(),
str.cend(),
rgx_pattern,
"");
return rtn;
}
This function takes in input a string and "fixes the spaces problem".
Here a demo
On a loop search for string " ," and if you find one replace that to ",":
std::string str = "...";
while( true ) {
auto pos = str.find( " ," );
if( pos == std::string::npos )
break;
str.replace( pos, 2, "," );
}
Do the same for " .". If you need to process different space symbols like tab use regex and proper group.
I don't know how to use regex for C++, also not sure if C++ supports PCRE regex, anyway I post this answer for the regex (I could delete it if it doesn't work for C++).
You can use this regex:
\s+(?=[,.])
Regex demo
First, there is no need to use a vector of char: you could very well do the same by using an std::string.
Then, your approach can't work because your copy is independent of the position of the space. Unfortunately you have to remove only spaces around the punctuation, and not those between words.
Modifying your code slightly you could delay copy of spaces waiting to the value of the first non-space: if it's not a punctuation you'd copy a space before the character, otherwise you just copy the non-space char (thus getting rid of spaces.
Similarly, once you've copied a punctuation just loop and ignore the following spaces until the first non-space char.
I could have written code. It would have been shorter. But i prefer letting you finish your homework with full understanding of the approach.
I did a program to remove a group of Characters From a String. I have given below that coding here.
void removeCharFromString(string &str,const string &rStr)
{
std::size_t found = str.find_first_of(rStr);
while (found!=std::string::npos)
{
str[found]=' ';
found=str.find_first_of(rStr,found+1);
}
str=trim(str);
}
std::string str ("scott<=tiger");
removeCharFromString(str,"<=");
as for as my program, I got my output Correctly. Ok. Fine. If I give a value for str as "scott=tiger" , Then the searchable characters "<=" not found in the variable str. But my program also removes '=' character from the value 'scott=tiger'. But I don't want to remove the characters individually. I want to remove the characters , if i only found the group of characters '<=' found. How can i do this ?
The method find_first_of looks for any character in the input, in your case, any of '<' or '='. In your case, you want to use find.
std::size_t found = str.find(rStr);
This answer works on the assumption that you only want to find the set of characters in the exact sequence e.g. If you want to remove <= but not remove =<:
find_first_of will locate any of the characters in the given string, where you want to find the whole string.
You need something to the effect of:
std::size_t found = str.find(rStr);
while (found!=std::string::npos)
{
str.replace(found, rStr.length(), " ");
found=str.find(rStr,found+1);
}
The problem with str[found]=' '; is that it'll simply replace the first character of the string you are searching for, so if you used that, your result would be
scott =tiger
whereas with the changes I've given you, you'll get
scott tiger
int main()
{
char* a = " 'Fools\' day' ";
char* b[64];
sscanf(a, " '%[^']s ", b);
printf ("%s", b);
}
--> puts "Fools" in b
Obviously, I want to have "Fools' day" in b. Can I tell sscanf() not to consider escaped apostrophes as the end of the character sequence?
Thanks!
No. Those functions just read plain old characters. They don't interpret the contents according to any escaping rules because there's nothing to escape from — quotation marks, apostrophes, and backslashes aren't special in the input string.
You'll have to use something else to parse your string. You can write a little state machine to read the string one character at a time, keeping track of whether the previous character was a backslash. (Don't just scan to the next apostrophe and then look one character backward; if you're allowed to escape backslashes as well as apostrophes, then you could end up re-scanning all the way back to the start of the string to see whether you have an odd or even number of escape characters. Always parse strings forward, not backward.)
Replace
char* a = " 'Fools\' day' ";
with
char* a = " 'Fools' day' ";
The ' character isn't special inside a C string (although it is special within a single char). So there is not need to escape it.
Also, if all you want is "Fools' day", why put the extra 's at the start and end? Maybe you are confusing C strings with those in some other language?
Edit:
As Rob Kennedy's comment says, I was assuming you are supplying the string yourself. Otherwise, see Rob's answer.
Why on earth would you write such a thing, instead of using std::string? Since your question is tagged C++.
int main(int argc, char* argv[])
{
std::string a = " 'Fools' day' ";
std::string b(a.begin() + 2, std::find(a.begin() + 2, a.end(), ' '));
std::cout << b;
std::cin.get();
}
Edit: Oh wait a second, you want to read a string within a string? Just use escaped double quotes, e.g.
int main(int argc, char* argv[]) {
std::string a = " \"Fool's day\" ";
auto it = std::find(a.begin(), a.end(), '"');
std::string b(it, std::find(it, a.end(), '"');
std::cout << b;
}
If the user put the string in, they won't have to escape single quotes, although they would have to escape double quotes, and you'd have to make your own system for that.