C++ 如何连接字符串和常量字符？
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How concatenate a string and a const char?
提问by xRobot
I need to put "hello world" in c. How can I do this ?
我需要将“hello world”放在 c 中。我怎样才能做到这一点 ？
string a = "hello ";
const char *b = "world";
const char *C;
回答by Griwes
string a = "hello ";
const char *b = "world";
a += b;
const char *C = a.c_str();
or without modifying a:
或不修改a：
string a = "hello ";
const char *b = "world";
string c = a + b;
const char *C = c.c_str();
Little edit, to match amount of information given by 111111.
小编辑，以匹配111111 提供的信息量。
When you already have strings (or const char *s, but I recommend casting the latter to the former), you can just "sum" them up to form longer string. But, if you want to append something more than just string you already have, you can use stringstreamand it's operator<<, which works exactly as cout's one, but doesn't print the text to standard output (i.e. console), but to it's internal buffer and you can use it's .str()method to get std::stringfrom it.
当您已经有strings （或const char *s，但我建议将后者转换为前者）时，您可以将它们“求和”以形成更长的字符串。但是，如果您想附加的不仅仅是您已经拥有的字符串，您可以使用stringstreamand it's operator<<，它的工作原理与cout's one完全一样，但不会将文本打印到标准输出（即控制台），而是打印到它的内部缓冲区你可以使用它的.str()方法从中获取std::string。
std::string::c_str()function returns pointer to const charbuffer (i.e. const char *) of string contained within it, that is null-terminated. You can then use it as any other const char *variable.
std::string::c_str()函数返回指向const char缓冲区（即const char *）中包含的字符串的指针，即以空字符结尾。然后您可以将其用作任何其他const char *变量。
回答by 111111
if you just need to concatenate then use the operator +and operator +=functions
如果您只需要连接，则使用operator +和operator +=函数
#include <string>
///...
std::string str="foo";
std::string str2=str+" bar";
str+="bar";
However if you have a lot of conacatenation to do then you can use a string stream
但是，如果您有很多连接要做，那么您可以使用字符串流
#include <sstream>
//...
std::string str1="hello";
std::stringstream ss;
ss << str1 << "foo" << ' ' << "bar" << 1234;
std::string str=ss.str();
EDIT: you can then pass the string to a C function taking a const char *with c_str().
编辑：然后您可以将字符串传递给const char *带有 with的 C 函数c_str()。
my_c_func(str1.c_str());
and If the C func takes a non const char * or require ownership you can do the following
如果 C func 采用非 const char * 或需要所有权，您可以执行以下操作
char *cp=std::malloc(str1.size()+1);
std::copy(str1.begin(), str2.end(), cp);
cp[str1.size()]='##代码##';
