invalid conversion from ‘char’ to ‘const char*' problem

I am having a problem with my code. I am writing a program to read an input from a file(just 50 lines of three digits numbers each) and then put it into a 2 dim array where a row is going to be a whole number where colums are going to be the numbers in 1st, 2nd and 3rd position (it is for Project Euler)

I succeed in reading the inputs from a file. But then when i try to convert the numbers in a string in doesnt work because it gives me the invalid conversion error.

The code is:

Code:

    #include <iostream>
    #include <fstream>
    #include <string>
    #include <stdlib.h>
    
    using namespace std;
    
    
    	    fstream myfile ("keylog.txt");
    	    string tries[60];
    	    string line;
    	    char codes[50][3];
    	    int i = 0;
    	    int j = 0;
    	    int code[50][3];
    
    	    while(myfile.good()){
    		    getline(myfile, line);
    		    tries[i] = line;
    		    i++;}
    
    	    for(i = 0; i < 50; i++){
    		    for(j = 0; j < 3; j++){
   			    code[i][j] = atoi( tries[i][j] );
    		    }
    	    }
           return 0;
    }

It compiles with the following error

keylog.cpp: In function ‘int main()’:
keylog.cpp:24:35: error: invalid conversion from ‘char’ to ‘const char*’
keylog.cpp:24:35: error: initializing argument 1 of ‘int atoi(const char*)’

I have been playing with this couple of hours but I could not figure out what it is.
Any help would be appreciated.

Best regards
Mike

your call to getline may as well just be tries[i]; the line variable is uneeded.

Originally Posted by rogster001

Your tries array is declared as one dimension but then you try and use it like it has 2 dimensions

tries is an array of std::strings; therefore, tries[ i ] is a string, and tries[ i ][ j ] is a char.

To the OP: The function atoi expects a const char*, and you are giving it a char. To compile this, you need to give it the address of (&) tries[ i ][ j ].

duh yes, not seeing that, apologies, but he should still test the length

Originally Posted by kuci

I am writing a program to read an input from a file(just 50 lines of three digits numbers each) and then put it into a 2 dim array where a row is going to be a whole number where colums are going to be the numbers in 1st, 2nd and 3rd position (it is for Project Euler)

It sounds like you just want to subtract '0', not use atoi.

Originally Posted by Ushakal

To compile this, you need to give it the address of (&) tries[ i ][ j ].

Note that just because it compiles does not mean that it is correct.

Originally Posted by Ushakal

To the OP: The function atoi expects a const char*, and you are giving it a char. To compile this, you need to give it the address of (&) tries[ i ][ j ].

This will cause undefined behavior. atoi is for C-style strings only, and not individual characters.
Never try to pass individual characters to atoi in any way or form.

Originally Posted by Elysia

This will cause undefined behavior. atoi is for C-style strings only, and not individual characters.
Never try to pass individual characters to atoi in any way or form.

Is that because atoi searches the string for the first numerical character (that is, '0' <= c && c <= '9'), then continues to read the string until it encounters a non-numerical character or the null terminating character, which may occur at any point in the following bytes of memory after the location of the single char (thus atoi may return an unexpected value)?

Originally Posted by Ushakal

Is that because atoi searches the string for the first numerical character (that is, '0' <= c && c <= '9'), then continues to read the string until it encounters a non-numerical character or the null terminating character, which may occur at any point in the following bytes of memory after the location of the single char (thus atoi may return an unexpected value)?

Yes, but the undefined behaviour is not because "atoi may return an unexpected value", but because atoi may end up reading beyond the bounds of the array.

Originally Posted by laserlight

Yes, but the undefined behaviour is not because "atoi may return an unexpected value", but because atoi may end up reading beyond the bounds of the array.

I see. Alright, thanks.

Originally Posted by Ushakal

Is that because atoi searches the string for the first numerical character (that is, '0' <= c && c <= '9'), then continues to read the string until it encounters a non-numerical character or the null terminating character, which may occur at any point in the following bytes of memory after the location of the single char (thus atoi may return an unexpected value)?

Yes, hence the why it requires a C-style string, not a char.