动态为char *分配内存时出错

Question

So the main problem is there is run time error in the code:

char *wordBank[]= {new char[numWords+1]};
char  buffer1[41];

for(int i=0; i<numWords;i++){
    ifile >> buffer1;
    int len = strlen(buffer1);
    cout << buffer1<<"and"<<len <<endl;
    wordBank[i] = new char[len + 1];
    strncpy(wordBank[i], buffer1,len);
    cout << wordBank[i]<<"and"<<len <<endl;
}

is it starts to mess up with what is in wordBank. It gets the words from a txt file into buffer1 and then copy if into the dynamically allocated char* array of wordBank. However I always get segmentation fault and the words are all incorrect. What did I do wrong?

Answer 1

You can simplify the code using C++ instead of C:

vector<string> wordBank(numWords);
string buffer1;
for (int i = 0; i < numWords; i++) {
  ifile >> buffer1;
  size_t len = buffer1.length();
  cout << buffer1 << "and" << len << endl;
  wordBank[i] = buffer1;
  cout << wordBank[i] << "and" << len << endl;
}

Or even simpler, but adding error checking:

vector<string> wordBank(numWords);
for (int i = 0; i < numWords; i++) {
  if (ifile >> wordBank[i])
    cout << wordBank[i] << "and" << len << endl;
  else { // no more words
    wordBank.resize(i); // chop off the unused portion
    break;
  }
}

Answer 2

This line is wrong:

char *wordBank[] = {new char[numWords+1]};

wordBank is an array with one element, the value of that one element is a pointer to a character array with numWords+1 characters. When you access wordBank[1] you're outside the bounds of the array, which results in undefined behavior.

What you apparently want is:

char **wordBank = new char*[numWords];

This creates a dynamically-allocated array of numWords char* elements, which you will then assign in the for loop.

I don't see any need for numWords+1 .