从 c++ 中的 function 返回二维字符数组并打印

Question

This is my code and I want to return 2D dimension array [10][8] and [10][20] from my function, but i get an error.! (Segmentation fault).

Please help me.. I need this for my project. Finally i want to print this array and I cant do this because of the error.

Can someone help me fix this and print that?

#include <iostream>
#include <cstdlib>
#include <ctime>
#include <cstring>

using namespace std;

char **getWords(int level)
{
    if (level == 1)
    {
        char **words = new char *[8];
        strcpy(words[0], "Pakistan");
        strcpy(words[1], "Portugal");
        strcpy(words[2], "Tanzania");
        strcpy(words[3], "Thailand");
        strcpy(words[4], "Zimbabwe");
        strcpy(words[5], "Cameroon");
        strcpy(words[6], "Colombia");
        strcpy(words[7], "Ethiopia");
        strcpy(words[8], "Honduras");
        strcpy(words[9], "Maldives");
        return words;
    }
    //For Hard Level
    else if (level == 2)
    {
        char **words = (char **)malloc(sizeof(char *) * 20);
        strcpy(words[0], "Tajikistan");
        strcpy(words[1], "Uzbekistan");
        strcpy(words[2], "Azerbaijan");
        strcpy(words[3], "Bangladesh");
        strcpy(words[4], "Luxembourg");
        strcpy(words[5], "Madagascar");
        strcpy(words[6], "Mauritania");
        strcpy(words[7], "Montenegro");
        strcpy(words[8], "Mozambique");
        strcpy(words[9], "New Zealand");

        return words;
    }
}

int main()
{
    getWords(1);

    return 0;
}

Answer 1

By doing

char **words = new char *[10];

You are only allocating memory for the pointers, not for the memory blocks where the actual strings are to be stored, you need to allocate memory for that too:

char **words = new char *[10]; //space for 10 pointers
        
for(int i = 0; i < 10; i++){
    words[i] = new char[10]; // space for 10 characters each line, 8 is not enough
}                            // you need at least 9 because of the ending nul byte

strcpy(words[0], "Pakistan");
strcpy(words[1], "Portugal");
//...

In main, assing them to a pointer to pointer and print them as if it was an array of strings:

char** words = getWords(1);

for(int i = 0; i < 10; i++){
    std::cout << words[i] << std::endl;
}

Live demo

The same goes for the second part which uses malloc .

char **words = (char**)malloc(sizeof *words * 10); //space for 10 pointers

for(int i = 0; i < 10; i++){
    words[i] = (char*) malloc(20); //space for 20 characters each line
}

Live demo

In a normal situation, when the program doesn't end right away you would have to free the memory:

For memory allocated with new :

for (int i = 0; i < 10; i++) 
{
    delete words[i];
}
delete words;

For the memory allocated with malloc :

for(int i = 0; i < 10; i++)
{
    free(words[i]);
}
free(words);  

This can be tricky in your case because you return 2 types of memory allocation deppending on the option you pass as parameter, my advice is that you use that same option to choose how to deallocate the memory.

PS: Using C++ containers like std::vector and std::string would make your job easier, you wouldn't need to handle the memory yourself.

Answer 2

Use of

 char **words =new char*[8];
 strcpy(words[0],"Pakistan");

is a problem since you have not allocated memory for words[0] .

It's analogous to

 char* cp; /// Uninitialized pointer
 strcpy(cp,"Pakistan");

You'll have to allocate memory for words[0] , words[1] , etc. before you use them in the call to strcpy .

More importantly, change your strategy, and use std::vector<std::sting> instead. That makes your code simpler and removes the burden of allocating and dealloating memory from application code.

std::vector<std::string> getWords(int level)
{
     std::vector<std::string> words;
     if (level==1)
     {
         words.push_backl("Pakistan");
         // etc.

     
     return words;
}