如何在 C++ 中将 int 附加到字符串？
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How do you append an int to a string in C++?
提问by Sebastian Redl
int i = 4;
string text = "Player ";
cout << (text + i);
I'd like it to print Player 4.
我想打印出来Player 4。
The above is obviously wrong but it shows what I'm trying to do here. Is there an easy way to do this or do I have to start adding new includes?
以上显然是错误的，但它显示了我在这里尝试做的事情。有没有一种简单的方法可以做到这一点，还是我必须开始添加新的包含？
回答by headmyshoulder
With C++11, you can write:
使用 C++11，您可以编写：
#include <string> // to use std::string, std::to_string() and "+" operator acting on strings
int i = 4;
std::string text = "Player ";
text += std::to_string(i);
回答by Sebastian Redl
Well, if you use cout you can just write the integer directly to it, as in
好吧，如果您使用 cout，您可以直接将整数写入它，如
std::cout << text << i;
The C++ way of converting all kinds of objects to strings is through string streams. If you don't have one handy, just create one.
将各种对象转换为字符串的 C++ 方式是通过字符串流。如果你手头没有，那就创建一个。
#include <sstream>
std::ostringstream oss;
oss << text << i;
std::cout << oss.str();
Alternatively, you can just convert the integer and append it to the string.
或者，您可以只转换整数并将其附加到字符串。
oss << i;
text += oss.str();
Finally, the Boost libraries provide boost::lexical_cast, which wraps around the stringstream conversion with a syntax like the built-in type casts.
最后，Boost 库提供了boost::lexical_cast，它使用类似于内置类型转换的语法围绕字符串流转换。
#include <boost/lexical_cast.hpp>
text += boost::lexical_cast<std::string>(i);
This also works the other way around, i.e. to parse strings.
这也适用于其他方式，即解析字符串。
回答by Eric
printf("Player %d", i);
(Downvote my answer all you like; I still hate the C++ I/O operators.)
（你喜欢什么就对我的答案投反对票；我仍然讨厌 C++ I/O 操作符。）
:-P
:-P
回答by Fire Lancer
These work for general strings (in case you do not want to output to file/console, but store for later use or something).
这些适用于一般字符串（如果您不想输出到文件/控制台，而是存储以供以后使用或其他东西）。
boost.lexical_cast
boost.lexical_cast
MyStr += boost::lexical_cast<std::string>(MyInt);
String streams
字符串流
//sstream.h
std::stringstream Stream;
Stream.str(MyStr);
Stream << MyInt;
MyStr = Stream.str();
// If you're using a stream (for example, cout), rather than std::string
someStream << MyInt;
回答by Jason Baker
For the record, you can also use a std::stringstreamif you want to create the string before it's actually output.
作为记录，std::stringstream如果您想在实际输出之前创建字符串，也可以使用 a 。
回答by jjnguy
cout << text << " " << i << endl;
回答by Richard
Your example seems to indicate that you would like to display the a string followed by an integer, in which case:
您的示例似乎表明您希望显示后跟整数的字符串，在这种情况下：
string text = "Player: ";
int i = 4;
cout << text << i << endl;
would work fine.
会工作得很好。
But, if you're going to be storing the string places or passing it around, and doing this frequently, you may benefit from overloading the addition operator. I demonstrate this below:
但是，如果您要存储字符串位置或传递它，并且经常这样做，您可能会从重载加法运算符中受益。我在下面演示：
#include <sstream>
#include <iostream>
using namespace std;
std::string operator+(std::string const &a, int b) {
std::ostringstream oss;
oss << a << b;
return oss.str();
}
int main() {
int i = 4;
string text = "Player: ";
cout << (text + i) << endl;
}
In fact, you can use templates to make this approach more powerful:
实际上，您可以使用模板使这种方法更强大：
template <class T>
std::string operator+(std::string const &a, const T &b){
std::ostringstream oss;
oss << a << b;
return oss.str();
}
Now, as long as object bhas a defined stream output, you can append it to your string (or, at least, a copy thereof).
现在，只要对象b具有定义的流输出，您就可以将其附加到您的字符串（或至少是其副本）。
回答by Daniel James
Another possibility is Boost.Format:
另一种可能性是Boost.Format：
#include <boost/format.hpp>
#include <iostream>
#include <string>
int main() {
int i = 4;
std::string text = "Player";
std::cout << boost::format("%1% %2%\n") % text % i;
}
回答by Brian Lenoski
For the record, you could also use Qt's QStringclass:
作为记录，您还可以使用 Qt 的QString类：
#include <QtCore/QString>
int i = 4;
QString qs = QString("Player %1").arg(i);
std::cout << qs.toLocal8bit().constData(); // prints "Player 4"
回答by Robert Parcus
Here a small working conversion/appending example, with some code I needed before.
这是一个小的工作转换/附加示例，其中包含我以前需要的一些代码。
#include <string>
#include <sstream>
#include <iostream>
using namespace std;
int main(){
string str;
int i = 321;
std::stringstream ss;
ss << 123;
str = "/dev/video";
cout << str << endl;
cout << str << 456 << endl;
cout << str << i << endl;
str += ss.str();
cout << str << endl;
}
the output will be:
输出将是：
/dev/video
/dev/video456
/dev/video321
/dev/video123
Note that in the last two lines you save the modified string before it's actually printed out, and you could use it later if needed.
请注意，在最后两行中，您在实际打印出来之前保存了修改后的字符串，如果需要，您可以稍后使用它。
