C++ string to fixed sized char array possible? - c++

Question

Hi i have the following code:
char msg[10000];
string mystr = "hello";
I want to put mystr into msg. Is there a way to do that? I tried all sorts of methods, but keep getting:
incompatible types in assignment of 'const char*' to char [10000]'
I tried:
msg = mystr.c_str();
and
msg = (char[10000])mystr;
to no avail.

Answer 1

You can try std::copy for this. Something like:
std::copy(mystr.begin(), mystr.end(), msg);
I would avoid C string functions like mempcy and strcpy in C++.

Answer 2

Take a look at string::copy - it takes a string an puts it into an array.
In your case it would be:
std::size_t length = mystr.copy(msg,10000);
msg[length]='\0';

Answer 3

char msg[10000];
string mystr = "hello";
strcpy(msg, mystr.c_str());
cout<<msg;

Answer 4

Use copy member function of std::string:
size_t len = mystr.copy(msg, (sizeof msg)-1);
msg[len] = 0;

Answer 5

String assignment in C is different. You have to copy the bytes into your destination string.
memcpy_s(msg, 1000, mystr.c_str(), mystr.length()) // safe windows version
memcpy(msg, mystr.c_str(), mystr.length()) // unix version

Answer 6

Use strcpy function :
http://www.cplusplus.com/reference/clibrary/cstring/strncpy/
strncpy(msg, mystr.c_str(), sizeof msg / sizeof msg[0]);
msg[sizeof msg / sizeof msg[0] - 1] = 0; // null-terminate in case of truncation

Answer 7

Compilers sometimes produce wonky error messages for array types.
Here's an accumulation of previous answers into a paste-and-compile program.
#include <string>
#include <iostream>
#if 1
int main(int argc, char **argv)
{
using std::cout;
using std::endl;
char msg[1000] = {0}; // initialize to 0 here since we're printing below
// the <type> <array-name>[<size>] = {0} just fills a POD struct or an array with 0s
std::string mystr = "hello";
// if, at some point, you have things changing "mystr"
// you'll need to make sure that it will fit in msg[]
cout << "Before strcpy: \"" << msg << "\"" << endl;
// I'll just finish the statement in mystr...
mystr += " world!";
if(mystr.length() < sizeof(msg)){
strcpy(
msg, // <- put in here until we find a '\0'
mystr.c_str() // <- take from here (which could be a temporary buffer)
);
}
//MSC will complain about strcpy being unsafe
//
// you can use the below instead (if you really feel the need to), which is
// the MS-specific equivalent to the above.
/*
strcpy_s(
msg, // <- put in here until we find a '\0' or the size limit is reached
sizeof(msg), // <- don't put any more than this many chars in msg
mystr.c_str() // <- take from here
);
*/
cout << "After strcpy: \"" << msg << "\"" << endl;
return 0;
}
#else
// Similarly, using wchar_t (a usually non-byte-sized character type)
//
// note where the divisions occurr
int main(int argc, char **argv)
{
using std::wcout;
using std::endl;
wchar_t msg[1000] = {0};
std::wstring mystr = L"hello";
wcout << "Before strcpy: \"" << msg << "\"" << endl;
mystr += L" world";
if(mystr.length() < (sizeof(msg)/sizeof(wchar_t))){
// mystr wil fit!
wcscpy(
msg, // <- put in here until we find a '\0'
mystr.c_str() // <- take from here (which could be a temporary buffer)
);
}
// Similar to the char case in the first preprocessor block
/*
wcscpy_s(
msg, // <- put in here until we find a '\0' or the size limit is reached
sizeof(msg)/sizeof(wchar_t), // <- don't put any more than this many wchar_ts in msg
mystr.c_str() // <- take from here
);
*/
wcout << "After strcpy: \"" << msg << "\"" << endl;
return 0;
}
#endif
I shall leave it to you to read the documentation on all related functions.