I'd like to add a timestamp to the filename in this part of my code:
takeScreenshot( "screenshot.png" );
But all ways of doing this that I've found seem unnecessarily long and complicated. E.g. creating a new string, loading a time struct, converting an element of the time struct to a char array and appending it to the string.
Is there a short way to accomplish this? Most other languages would have some simple solution like:
takeScreenshot( sprintf( "screenshot-%d.png", time() ) );
Is there one in C++? The time format doesn't matter.
Concatenating a string is long and complicated, under the hood.
A nice way is to use std::stringstream which overloads << for concatenation:
std::stringstream ss;
ss << "screenshot-" << time() << ".png";
std::string s = ss.str();
and format time() to personal taste.
You can use stringstream or just use + operator between strings:
takeScreenshot("screenshot-" + time() + ".png");
Related
I am somewhat new to C++ and my background is in Java. I am working on a hdc printing method.
I would like to know the best practice for concatenating a combination of strings and ints into one CString. I am using MFC's CString.
int i = //the current page
int maxPage = //the calculated number of pages to print
CString pages = ("Page ") + _T(i) + (" of ") + _T(maxPage);
I would like it to look like 'Page 1 of 2'. My current code does not work. I am getting the error:
Expression must have integral or enum type
I have found more difficult ways to do what I need, but I want to know if there is a simple way similar to what I am trying. Thanks!
If that's MFC's CString class, then you probably want Format which is a sprintf-alike for it:
CString pages;
pages.Format(_T("Page %d of %d"), i, maxPage);
i.e. you can assemble the string using regular printf-format specifiers substituting in the numbers at runtime.
You can use also stringstream classes
#include <sstream>
#include <string>
int main ()
{
std::ostringstream textFormatted;
textFormatted << "Page " << i << " of " << maxPage;
// To convert it to a string
std::string s = textFormatted.str();
return 0;
}
std::string has all you need:
auto str = "Page " + std::to_string(i) + " of " + std::to_string(maxPage);
As stated correctly in the comment, you can access the underlying C-string via str.c_str(). Here is a live working example.
If you have C++11 you can use std::to_string: std::string pages = std::string("Page ") + std::to_string(i) + (" of ") + std::to_string(maxPage);
If you don't have C++11 you can use an ostringstream or boost::lexical_cast.
In C++, how can I convert a data of type float64 to a string without losing any of the data in float64? I need it to not only be converted to a string, but add a string to either side of the number and then sent to be written in a file.
Code:
string cycle("---NEW CYCLE ");
cycle+=//convert float64 to string and add to cycle
cycle+= "---\r\n";
writeText(cycle.c_str()); //writes string to txt file
Thanks.
The usual way of converting numbers to std::strings is to use std::ostringstream.
std::string stringify(float value)
{
std::ostringstream oss;
oss << value;
return oss.str();
}
// [...]
cycle += stringify(data);
You should use sprintf. See documentation here C++ Reference.
As an example it would be something like:
char str[30];
float flt = 2.4567F;
sprintf(str, "%.4g", flt );
Also I would use string::append to add the string. See here .
UPDATE
Updated code according to comment.
You can use sprintf to format the string.
I just started learning C++ in Qt and I was wondering how can I put a variables result in a string? I'm trying to use this for a simple application where someone puts their name in a text field then presses a button and it displays there name in a sentence. I know in objective-c it would be like,
NSString *name = [NSString stringWithFormatting:#"Hello, %#", [nameField stringValue]];
[nameField setStringValue:name];
How would I go about doing something like this with C++? Thanks for the help
I assume we're talking about Qt's QString class here. In this case, you can use the arg method:
int i; // current file's number
long total; // number of files to process
QString fileName; // current file's name
QString status = QString("Processing file %1 of %2: %3")
.arg(i).arg(total).arg(fileName);
See the QString documentation for more details about the many overloads of the arg method.
You don´t mention what type your string is. If you are using the standard library then it would be something along the lines of
std::string name = "Hello, " + nameField;
That works for concatenating strings, if you want to insert other complex types you can use a stringstream like this:
std::ostringstream stream;
stream << "Hello, " << nameField;
stream << ", here is an int " << 7;
std::string text = stream.str();
Qt probably has its own string types, which should work in a similar fashion.
I would use a stringstream but I'm not 100% sure how that fits into your NSString case...
stringstream ss (stringstream::in);
ss << "hello my name is " << nameField;
I think QString has some nifty helpers that might do the same thing...
QString hello("hello ");
QString message = hello % nameField;
You could use QString::sprintf. I haven't found a good example of it's use yet, though. (If someone else finds one, feel free to edit it in to this answer).
You might be interested in seeing information about the difference between QString::sprintf and QString::arg.
I have two char* strings and a char* literal that I need to combine into a single std::string. Below is what I am doing. It works, but I don't like the way it looks (3 lines to accomplish it). I am wondering if there is a better way to do it...
std::string strSource = _szImportDirectory;
strSource += "\\";
strSource += _szImportSourceFile;
Thanks for you help!
std::string strSource = std::string(_szImportDirectory) + "\\" + _szImportSourceFile;
Is one obvious way.
Another way is to use std::stringstream:
std::stringstream s;
s << _szImportDirectory << '\\' + _szImportSourceFile;
std::string strSource = s.str()
That's the most flexible and maintainable way to do it but it still requires three lines.
Something like this?
std::string str = std::string(_szImportDirectory).append("\\").append(_szImportSourceFile);
PS: updated with correct code
I'm using the function time() in order to get a timestamp in C++, but, after doing so, I need to convert it to a string. I can't use ctime, as I need the timestamp itself (in its 10 character format). Trouble is, I have no idea what form a time_t variable takes, so I don't know what I'm converting it from. cout handles it, so it must be a string of some description, but I have no idea what.
If anyone could help me with this it'd be much appreciated, I'm completely stumped.
Alternately, can you provide the output of ctime to a MySQL datetime field and have it interpreted correctly? I'd still appreciate an answer to the first part of my question for understanding's sake, but this would solve my problem.
time_t is some kind of integer. If cout handles it in the way you want, you can use a std::stringstream to convert it to a string:
std::string timestr(time_t t) {
std::stringstream strm;
strm << t;
return strm.str();
}
I had the same problem. I solved it as follows:
char arcString [32];
std::string strTmp;
// add start-date/start-time
if (strftime (&(arcString [0]), 20, "%Y-%m-%d_%H-%M-%S", (const tm*) (gmtime ((const time_t*) &(sMeasDocName.sStartTime)))) != 0)
{
strTmp = (char*) &(arcString [0]);
}
else
{
strTmp = "1970-01-01_00:00:00";
}
Try sprintf(string_variable, "%d", time) or std::string(itoa(time))?
http://www.codeguru.com/forum/showthread.php?t=231056
In the end time_t is just an integer.