Programming Forums > Application Development > C++

Mcoy · Nov 13th, 2006, 9:09 PM

string temp;
    char temp2[3];
    int num_of_values;
    
    getline (myfile,temp);
    
    for(int i(0); i < 3; i++)
    {
            temp2[i] = temp[i];
    }
    
    num_of_values = atoi(temp2);

The goal of the above code was to read a line from a file (with the getline function) and convert it from string type to integer type with atoi(). When supplying the atoi function with the string, the compiler gave me an error saying that atoi did not accept strings, only const char*s. So I had to use the for loop that you see in my code to change each letter from the string to a char array. -Seems very redundant to me considering a string is simply a character array, or am I mistaken?
What is a better/more efficient/intuitive way to read integers into my program from a file?

DaWei · Nov 13th, 2006, 9:53 PM

Your terminology is too fuzzy. An array of char, terminated by a '\0', is often referred to as a string, and atoi would accept that. The C++ string class is something else, but you can access its array of char with ElStringo.c_str (). Atoi isn't a great choice, since an error will return the same thing as the value, zero, so you can't tell the difference. There are other things like strtol, etc., that work better. You might also wish to investigate string streams.

Narue · Nov 14th, 2006, 8:16 AM

>since an error will return the same thing as the value, zero, so you can't tell the difference
Not to mention undefined behavior if the value can't be represented by an int. atoi is only about two steps above gets on my eew-o-meter.

DaWei · Nov 14th, 2006, 8:34 AM

A whole two? ewwwwwwwwwwwww.

Nov 13th, 2006, 9:09 PM	#1
Mcoy Newbie Join Date: Mar 2006 Posts: 20 Rep Power: 0	About atoi function and const chars... (Toggle Plain Text) string temp; char temp2[3]; int num_of_values; getline (myfile,temp); for(int i(0); i < 3; i++) { temp2[i] = temp[i]; } num_of_values = atoi(temp2); string temp; char temp2[3]; int num_of_values; getline (myfile,temp); for(int i(0); i < 3; i++) { temp2[i] = temp[i]; } num_of_values = atoi(temp2); The goal of the above code was to read a line from a file (with the getline function) and convert it from string type to integer type with atoi(). When supplying the atoi function with the string, the compiler gave me an error saying that atoi did not accept strings, only const char*s. So I had to use the for loop that you see in my code to change each letter from the string to a char array. -Seems very redundant to me considering a string is simply a character array, or am I mistaken? What is a better/more efficient/intuitive way to read integers into my program from a file?

Nov 13th, 2006, 9:53 PM	#2
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	Your terminology is too fuzzy. An array of char, terminated by a '\0', is often referred to as a string, and atoi would accept that. The C++ string class is something else, but you can access its array of char with ElStringo.c_str (). Atoi isn't a great choice, since an error will return the same thing as the value, zero, so you can't tell the difference. There are other things like strtol, etc., that work better. You might also wish to investigate string streams. __________________ Abstraction doesn't make it impossible to write bad code; it makes it possible to write superior code. Contributor's Corner: Grumpy on C++ Exceptions DaWei on Pointers

Nov 14th, 2006, 8:16 AM	#3
Narue Professional Programmer Join Date: Sep 2005 Posts: 419 Rep Power: 4	>since an error will return the same thing as the value, zero, so you can't tell the difference Not to mention undefined behavior if the value can't be represented by an int. atoi is only about two steps above gets on my eew-o-meter. __________________ Even if the voices aren't real, they have some pretty good ideas.

Nov 14th, 2006, 8:34 AM	#4
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	A whole two? ewwwwwwwwwwwww. __________________ Abstraction doesn't make it impossible to write bad code; it makes it possible to write superior code. Contributor's Corner: Grumpy on C++ Exceptions DaWei on Pointers

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Programming Forums > Application Development > C++

About atoi function and const chars...