why my cpp code can't run?(about char*[])

Question

this is my code

the error is Segmentation fault,and i can't understand why

#include <iostream>
#include <cstdio>
#include <string>
#include <cstring> 

using namespace std;

int main(int argc, char* argv[])
{
    char* szword[100];

    int i = 0;

    do
    {
        cin >> szword[i];
        cout << szword[i];
        i++;
    }while(strcmp(szword[i - 1], "done"));

    cout << i + 1;

    return 0;
}

What is `char* szword[100];` supposed to be? I think its not what you actually wanted. If you want strings, use `std::string`, `std::vector` for a vector of strings — 463035818_is_not_an_ai, Jun 22 '21 at 11:02
Does this answer your question? [Why aren't variable-length arrays part of the C++ standard?](https://stackoverflow.com/questions/1887097/why-arent-variable-length-arrays-part-of-the-c-standard) — , Jun 22 '21 at 20:27

score 0 · Answer 1 · answered Jun 22 '21 at 11:25

For starters neither declaration from headers <cstdio> and <string> is used in your program. So you should remove these directives

#include <cstdio>
#include <string>

You declared an initialized array with the element type char *. Thus this statement

cin >> szword[i];

invokes undefined behavior because the pointer szword[i] has indeterminate value.

Moreover this call even if the argument of the operator will be correct

cin >> szword[i];

can fail. You should check whether it was successful. And I think there is no great sense to output the string "done".

Also in this statement

cout << i + 1;

you are outputting a value that is greater than the number of inputted strings.

If to use character arrays then your program could look the following way

#include <iostream>
#include <cstring>

int main() 
{
    const size_t N = 100;
    char szword[N][N];
    
    size_t i = 0;
    while ( std::cin.getline( szword[i], sizeof( szword[i] ) ) && 
            std::strcmp( szword[i], "done" ) != 0 )
    {
        std::cout << szword[i++] << '\n';
    }
    
    std::cout << i << '\n';
    
    return 0;
}

The program output might look like

Hello
World
2

score -1 · Answer 2 · answered Jun 22 '21 at 12:48

This below code works fine, if you want to use char *, for C++ string you can use the C++ version

C Version:

#include <iostream>
#include <cstdio>
#include <string>
#include <cstring> 

using namespace std;

int main(int argc, char* argv[])
{
  char *tmp;
  int i = 0;

do
{
    cin >> tmp;
    cout << tmp;
    i++;
}while(strcmp(tmp, "done"));

cout << i + 1;

return 0;
}

C++ Version:

#include <iostream>
#include <cstdio>
#include <string>
#include <cstring> 

using namespace std;

int main(int argc, char* argv[])
{
  string tmp;
  int i = 0;

do
{
    cin >> tmp;
    cout << tmp;
    i++;
}while(tmp != "done"));

cout << i + 1;

return 0;
}

why my cpp code can't run?(about char*[])

2 Answers2