How can I copy the contents of string to an array of char c++?

Question

So I have this issue

//This holds 5 messages submitted prev by the user, temporarily stored
string arrayOfMessages[5];

lets say

arrayOfMessages[0]="This is my message"//The message in the first position.

I need to copy arrayOfMessages[0] to an array of char like this one;

char message [20];

I tried using strcpy(message,arrayOfMessages[0]) but I get this error :

error: cannot convert 'std::__cxx11::string' {aka 'std::__cxx11::basic_string<char>'} to 'const char*'|

Anyone know how I can accomplish this or if I'm doing something wrong, I cant set the string to be a const char bc the message was imputed prev by the user so it changes every time you run the program thus cannot be a constant variable.

Does this answer your question? [Store c\_str() as char \*](https://stackoverflow.com/questions/20305611/store-c-str-as-char) — Mansoor, Jul 30 '20 at 10:07
`c_str()` is designed for this. But why do you need to copy, and what are you going to do if the source string is too long are the important questions. — john, Jul 30 '20 at 10:09
I´m no sure I understand how to use c_str(), mainly cus it requires strcpy and my variables cannot be const * so it wont copy — CHstudent22, Jul 30 '20 at 10:16
Read the first answer more closely, `strcpy(message,arrayOfMessages[0].c_str())`. — Mansoor, Jul 30 '20 at 10:42

Marko Borković · Accepted Answer · 2020-07-30T10:22:15.063

1

There are many ways of doing it

By using the c_str() function of the string class

string message = "This is my message";
const char *arr;
arr = message.c_str();

By copying all the characters from the string to the char array

string message = "This is my message";
char arr[200];
for(int i = 0; i < 200 && message[i] != '\0'; i++){
    arr[i] = message[i];
}

Be careful with the array sizes if you use the second approach. You can also make it a function in order to make it easier to use

 void copyFromStringToArr(char* arr, string str, int arrSize){
     for(int i = 0; i<arrSize && str[i] != '\0'; i++){
         arr[i] = str[i];
     }
 }

So in your case you can just call the function like this:

copyFromStringToArr(message,arrayOfMessages[0],20);

Also I am sure there are many more ways to do it but these are the ones I would use.

edited Jul 30 '20 at 10:22

answered Jul 30 '20 at 10:11

Marko Borković

1,884
1
7
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I cant use the either bc i have to the same for 5 messages i cant use const char * in the variable. And the second option wonk work bc the string is located in an array thus i cant no use message [i] to copy , this is a one dimensional array of 5 strings – CHstudent22 Jul 30 '20 at 10:13
You can still use the [i] you just have to do it like this for example: `arrayOfMessages[0][i]`. Because array of strings can be treated like a 2D array – Marko Borković Jul 30 '20 at 10:17

Rohan Bari · Answer 2 · 2020-07-30T10:20:45.597

0

To copy the contents of std::string into a char[], use c_str():

std::string str = "hello";

char copy[20];
strcpy(copy, str.c_str());

But the datatype of copy must be only char* and not const char*. If you want to assign it to a const char*, then you can use direct assignment:

std::string str = "hello";
const char *copy = str.c_str();

edited Jul 30 '20 at 10:20

answered Jul 30 '20 at 10:11

Rohan Bari

7,482
3
14
34

How can I copy the contents of string to an array of char c++?

2 Answers2