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What is the difference between atoi and stoi?
I know,
std::string my_string = "123456789"; In order to convert that string to an integer, you’d have to do the following:
const char* my_c_string = my_string.c_str(); int my_integer = atoi(my_c_string); C++11 offers a succinct replacement:
std::string my_string = "123456789"; int my_integer = std::stoi(my_string); 1). Are there any other differences between the two?
2). Efficiency and performance wise which one is better?
3). Which is safer to use?
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Using atoi() First, atoi() converts C strings (null-terminated character arrays) to an integer, while stoi() converts the C++ string to an integer. Second, the atoi() function will silently fail if the string is not convertible to an int , while the stoi() function will simply throw an exception.
std::stoi. Parses str interpreting its content as an integral number of the specified base, which is returned as an int value. If idx is not a null pointer, the function also sets the value of idx to the position of the first character in str after the number.
1 Answer. Show activity on this post. the only difference is that atoi casts the return value to int . There could be different behavior in error cases (when the string represents a value that is out of range of the type), since behavior is undefined for both.
In C++, the stoi() function converts a string to an integer value. The function is shorthand for “string to integer,” and C++ programmers use it to parse integers out of strings. The stoi() function is relatively new, as it was only added to the language as of its latest revision (C++11) in 2011.
1). Are there any other differences between the two?
I find std::atoi() a horrible function: It returns zero on error. If you consider zero as a valid input, then you cannot tell whether there was an error during the conversion or the input was zero. That's just bad. See for example How do I tell if the c function atoi failed or if it was a string of zeros?
On the other hand, the corresponding C++ function will throw an exception on error. You can properly distinguish errors from zero as input.
2). Efficiency and performance wise which one is better?
If you don't care about correctness or you know for sure that you won't have zero as input or you consider that an error anyway, then, perhaps the C functions might be faster (probably due to the lack of exception handling). It depends on your compiler, your standard library implementation, your hardware, your input, etc. The best way is to measure it. However, I suspect that the difference, if any, is negligible.
If you need a fast (but ugly C-style) implementation, the most upvoted answer to the How to parse a string to an int in C++? question seems reasonable. However, I would not go with that implementation unless absolutely necessary (mainly because of having to mess with char* and \0 termination).
3). Which is safer to use?
See the first point.
In addition to that, if you need to work with char* and to watch out for \0 termination, you are more likely to make mistakes. std::string is much easier and safer to work with because it will take care of all these stuff.
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