Segmentation Fault while printing char array through pointer in C

Question

I am brushing up some on C coding for embedded programming, and I can't figure out why the following is throwing a segmentation fault error. I thought that by checking whether the pointer is pointing to NULL would suffice, but it does not seem the case.

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

using namespace std;

char json[] = "Authentication:YERL90\nredLedBri:400\nredLedOn:true\n";
char inData[100];

void printBuffer(char * buf) {
    cout << "...printing buffer:" << endl;
    char * p = buf;
    while(p) {
        cout << *p << endl;
        p++;
    }
    cout << "...end printing" << endl;

}

void resetBuffer(char * buf)
{
  memset(&buf[0], 0, sizeof(buf));
}


int main()
{

   printBuffer(json);

   return 0;
}

Any ideas what went wrong?

Off topic: I would prefer for(char const *p = buf; *p; ++p) cout << *p << std::endl;. This way the scope of p is limited, p is pointer to const, which can prevent accident. Stepping is also on a dedicated place. BTW printBuffer should accept char const * buf, because it does not want to write into the buffer. Also in resetBuffer &buf[0] is unnecessary, you can write buf. The sizeof(buf) expression will be evaluated to the size of a pointer not as size of the array behind the pointer. You need to accept size there. Or google "Template parameter deduction from array dimensions" — Notinlist
– Notinlist, Commented Apr 15, 2020 at 10:51
@Notinlist Thanks for pointing that out. I will amend my code to reflect your suggestions. Cheers! — vtolentino
– vtolentino, Commented Apr 15, 2020 at 10:56
cout << "...printing buffer:" << endl; In C, a string literal cannot be the rightside operand of a << operator. Maybe you are using C++? — wildplasser
– wildplasser, Commented Apr 15, 2020 at 11:03
@wildplasser I am using cout only to debug the code. The code belongs originally to a MCU where I am planning to parse incoming JSON data via C. I find it easier to debug it with a remote compiler instead of uploading the file to the MCU all the time. — vtolentino
– vtolentino, Commented Apr 15, 2020 at 11:05

Mickael B. · Accepted Answer · 2020-04-15 10:42:17Z

1

You are checking the address instead of the value at the address.

Replace while(p) with while(*p)

answered Apr 15, 2020 at 10:42

Mickael B.

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