Getting multiple input files in C++ and saving it in an array

Question

I want to get an input of multiple txt files using ifstream and store it in char* array or vector. I have several test files named test1.txt, test2.txt, test3.txt... So I used a for loop and set file path (string) as "test" + to_string(i) + ".txt" When I get an input string from that text file using get line or >> and print it for testing, the text is printed correctly inside the for loop. I saved the string into the array by using statement like "array[i-1]=str;"

and then when I print the array outside the for loop, the outputs are all same- it prints the string of the last test file. I want to know why is it like this.

I tried changing array into vectors, but it works the same. If I don't use the for loop and set each of filePath and string variable, it works fine but I don't think it's a good way to do that for more than 10 cases.

int main() { 
 char* array[10];
 char str[100]; //it is for the sample cases I randomly made which does  not exceeds 99 chars 

 for(int i=1; i<10; i++){
        string filePath = "Test" + to_string(i) + ".txt";
        ifstream openFile(filePath.data());
        if(openFile.is_open()){
           openFile >> str;
           array[i-1] = str;
           cout << array[i-1] << endl; 
           openFile.close();
        } 
}

cout << array[0] << endl;
cout << array[5] << endl;
cout << array[6] << endl;
//then if I print it here the outputs are all same: string from Test10.
}

for example, if test1.txt = "a", test2.txt = "b" ... test9.txt="i", test10.txt="j"

inside the for loop it is printed correctly => a b c d ... j. but outside the for loop the output is all j.

On an unrelated note, if you have std::to_string then your std::ifstream constructor also can take a std::string as argument for the filename. They were both introduced at the same time (with the C++11 standard). — Some programmer dude
– Some programmer dude, Commented Apr 29, 2019 at 15:16

Some programmer dude · Accepted Answer · 2019-04-29 15:13:58Z

3

You make all pointers of array point to the very same place: The first character of str.

There are a couple of ways of solving this:

Make array an array of arrays that you read directly into
Dynamically allocate new memory for each string you read, and copy the string into it
A few others...
Or the solution I recommend: Use an std::array (or possibly std::vector) of std::string and read directly into the strings.

answered Apr 29, 2019 at 15:13

Some programmer dude

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