C++ 创建文本字符串和变量
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C++ create string of text and variables
提问by Hyman Farrow
I'm trying to do something very simple and yet, after an hour of so of searching a I can't find a suitable answer so I must be missing something fairly obvious.
我正在尝试做一些非常简单的事情，但是，经过一个小时的搜索后，我找不到合适的答案，所以我必须遗漏一些相当明显的东西。
I'm trying to dynamically create filenames for use with ifstream. Whilst I understand various methods are available of doing this, I have settled on creating a std::string, and the using stringname.c_str to convert to const.
我正在尝试动态创建用于 ifstream 的文件名。虽然我知道有各种方法可以做到这一点，但我已经决定创建一个 std::string，并使用 stringname.c_str 转换为 const。
The problem is however that I need to create the string with a mix of variables and predefined text values. I'm getting compiler errors, so this must be a syntax issue.
然而，问题是我需要创建混合变量和预定义文本值的字符串。我收到编译器错误，所以这一定是语法问题。
Pseudo
伪
std::string var = "sometext" + somevar + "sometext" + somevar;
Thanks!
谢谢！
回答by mgiuffrida
Have you considered using stringstreams?
您是否考虑过使用字符串流？
#include <string>
#include <sstream>
std::ostringstream oss;
oss << "sometext" << somevar << "sometext" << somevar;
std::string var = oss.str();
回答by David Schwartz
std::string var = "sometext" + somevar + "sometext" + somevar;
This doesn't work because the additions are performed left-to-right and "sometext"(the first one) is just a const char *. It has no operator+to call. The simplest fix is this:
这不起作用，因为添加是从左到右执行的，并且"sometext"（第一个）只是一个const char *. 它没有operator+打电话。最简单的修复是这样的：
std::string var = std::string("sometext") + somevar + "sometext" + somevar;
Now, the first parameter in the left-to-right list of +operations is a std::string, which has an operator+(const char *). That operator produces a string, which makes the rest of the chain work.
现在，从左到右的+操作列表中的第一个参数是 a std::string，它有一个operator+(const char *). 该运算符生成一个字符串，使链的其余部分工作。
You can also make all the operations be on var, which is a std::stringand so has all the necessary operators:
您还可以将所有操作都设置为 on var，它是 a std::string，因此具有所有必要的运算符：
var = "sometext";
var += somevar;
var += "sometext";
var += somevar;
回答by David Rinck
In C++11 you can use std::to_string:
在 C++11 中，您可以使用std::to_string：
std::string var = "sometext" + std::to_string(somevar) + "sometext" + std::to_string(somevar);
回答by Yury
See also boost::format:
#include <boost/format.hpp>
std::string var = (boost::format("somtext %s sometext %s") % somevar % somevar).str();
回答by Shocker
You can also use sprintf:
您还可以使用 sprintf：
char str[1024];
sprintf(str, "somtext %s sometext %s", somevar, somevar);
