使用C9.io和C ++的堆栈粉碎错误

Question

I am getting a Stack Smashing Error using the c9 compiler, and I looked up reasons for the error, which is supposedly buggy code/passing variables or something that isn't declared/initialized, but I cant find the error in my code...

I've stripped the following code of any unnecessary code that doesn't pertain to the error, and this is what I have:

#include <iostream>
#include <cstring>

using namespace std;

void checkWord(char *word, int size);

int main () {
    string word1 = "racecar";
    char wordArr[sizeof(word1)];
    strcpy(wordArr, word1.c_str());
    checkWord(wordArr, strlen(wordArr));

    string word2 = "something";
    char word2Arr[sizeof(word2)];
    strcpy(word2Arr, word2.c_str());
    checkWord(word2Arr, strlen(word2Arr));
}

void checkWord(char *wordArr, int size) {
    // cout << "Size1: " << size << endl;
    int workingSize;
    if ((size % 2) != 0) {
        workingSize = (size +1)/2;
    } else {
        workingSize = size/2;
    }
    char *p, *q;
    p = wordArr;
    q = wordArr+strlen(wordArr)-1;
    bool pal = true;
    for (int i = 0; i < workingSize; i++) {
        if (*p != *q) {
            pal = false;
        }
        p++;
        q--;
    }
}

Which gives me this error output:

*** stack smashing detected ***:/home/ubuntu/workspace/.c9/metadata/workspace/3_16Lab2.cpp.o terminated
bash: line 12: 48077 Aborted                 $file.o $args


Process exited with code: 134

Otherwise, the program executes without any issue and, in this instance, confirms whether or not the words "racecar" and "something" are palindromes or not.

Answer 1

You declare char wordArr[sizeof(word1)]; which is one char short. Sizeof gives the number of characters in the string, but you need one more for the trailing '\\0' .

As a consequence, you start overwriting memory that you don't own, and anything beyond that is random undefined behavior.

Answer 2

sizeof(word1) returns the number of bytes the variable word1 occupies, which has nothing to do with the length of the string it represents. You should use word1.length() + 1 to get the length of the string, including the terminating nul character. (Same of sizeof(word2) .)

A better solution would be to either change checkWord to take its first parameter as a const char *wordArr , and pass the word in using word1.c_str() , or just pass the string to checkWord and not use character pointers at all.