C++ segmentation fault and recurrent function

Question

In this program, I used a recurrent function which is Strlen. However, prompt tells me that it is

zsh: 
segmentation fault  ./Strlen5

Does anyone know why it happens ?

My Code:

#include <iostream>
using namespace std;

size_t Strlen(char* str) {
    size_t i = 0;
    if (str[i] != '\0') {
        i += 1;
        return 1 + Strlen(str);
    } else {
        return 0;
    }
}

void ShowLength(char* str) {
    cout << "length:\"" << str << "\" : " << Strlen(str) << endl; 
}

int main() {
    ShowLength("Hello");
    ShowLength("Titan");
}

You should use `const char *`. Also why not use a loop? Recursion on a long string could result in stack overflow. — Neil Kirk, Aug 26 '15 at 01:45

score 4 · Answer 1 · answered Aug 25 '15 at 22:31

You never increment your pointer. You need to start one index ahead each time you recurse.

return 1 + Strlen(str + 1);

Also you should use const char* instead of char*

#include <iostream>
using namespace std;

size_t Strlen(const char* str) {
    if (str[0] != '\0') {
        return 1 + Strlen(str + 1);
    } else {
        return 0;
    }
}

void ShowLength(const char* str) {
    cout << "length:\"" << str << "\" : " << Strlen(str) << endl; 
}

int main() {
    ShowLength("Hello");
    ShowLength("Titan");
}

Working demo

@Shion the i += 1 in the original was an attempt at that but does not work because you never use I and you dont pass I to the following iteration — pm100, Aug 25 '15 at 22:34

score 1 · Answer 2 · edited May 23 '17 at 11:58

By the way the reason you got a segmentation fault is due to how a function call is constructed.

Since you need to pass on the stack the arguments and the pointer to next the instruction after the call you "waste" a portion of your stack every time you call a function (until you return). This usually is not a problem, but if you call an infinite number of function one after the other you face a stack overflow.

Further reading: Why infinite recursion leads to seg fault

C++ segmentation fault and recurrent function

2 Answers2