Question about using string arrays as function parameters

Question

I am a novice, I encountered a little problem today, I hope to get someone's answer, thank you very much. Code show as below。

#include<iostream>
using namespace std;
void sub(char b[]){
    b[] = "world";    //I alse try b*/b,but it is not ok
}
int main(void){
    char a[10] = "hello";
    sub(a);
    cout<<a<<endl;

    system("pause");
    return 0;
}

error: expected primary-expression before ']' token b[] = "world"; ^ The error

I want the final output will be "world". The function sub() can run correctly. What should I do?

HaHaHaHa,you are right, i'm so careless.Next time I will pay attention. — Hide on bush
– Hide on bush, Commented Dec 12, 2021 at 15:40
Better to post the error message as text than only a picture. — chux
– chux, Commented Dec 12, 2021 at 15:42
Use strcpy to write into an existing char array (although you'd need more safety checks in a real program) — UnholySheep
– UnholySheep, Commented Dec 12, 2021 at 15:43
One doesn't simply assign to a char array. You have to use std::strcpy and friends. Plus, if this is really C++, then use std::strings instead of char[]. — Intelligent Shade of Blue
– Intelligent Shade of Blue, Commented Dec 12, 2021 at 15:44
b[] = "world"; //I alse try b*/b,but it is not ok -- You can't learn C++ properly by randomly trying things. C++ is one of the most difficult languages to learn, and it is best to learn it by utilizing peer-reviewed C++ books. — PaulMcKenzie
– PaulMcKenzie, Commented Dec 12, 2021 at 15:45

Sîn-iông Tè · Accepted Answer · 2021-12-13 11:28:21Z

1

strcpy(b, "world"); // need <string.h>

But I would use std::string (instead of c-string) directly.

#include<iostream>
#include<string>
using std::cout;
using std::string;

void sub(string &b){
    b = "world";
}

int main(){
    string a = "hello";
    sub(a);
    cout << a << endl; // output

    system("pause");
    return 0;
}

edited Dec 13, 2021 at 11:28

answered Dec 12, 2021 at 15:51

Sîn-iông Tè

263 bronze badges

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3 Comments

Hide on bush Over a year ago

Thanks you very much.Other question:If i don't want to use strcpy and string just using array as a function parameter.what should i do？

Sîn-iông Tè Over a year ago

@Hideonbush As far as I know, you just cannot assign a string literal to a c-string variable unless it's a declaration. However, you can assign characters one by one, like b[0] = 'w'; b[1] = 'o'; and so on.

Hide on bush Over a year ago

Ok,Thanks for the prompt reply.Next time,I will not assign a string literal to a c-string variable unless it's a declaration.

Moshe Levy · Accepted Answer · 2021-12-12 18:14:46Z

0

as other people told you it's not c++ style but c style, I will try to explain why it does not compile. when you write b[i] you tell the compiler: "please go to memory location b + sizeof(b type) * i", so when you write b[], the compiler can't understand what you want.

answered Dec 12, 2021 at 18:14

Moshe Levy

18212 bronze badges

1 Comment

Hide on bush Over a year ago

Thanks, good explanation. So b[i] can only be assigned to a char type not string.

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