Question

What’s the safest and best way to retrieve an unsigned long from a string in C++?

I know of a number of possible methods.

First, converting a signed long taken from atol.

char *myStr; // Initalized to some value somehow.
unsigned long n = ((unsigned)atol(myStr));

The obvious problem with this is, what happens when the value stored in myStr is larger than a signed long can contain? What does atol retrieve?

The next possibility is to use strtoul.

char *myStr; // Initalized to some value somehow.
unsigned long n = strtoul(myStr, 0, 10);

However, this is a little over complicated for my needs. I’d like a simple function, string in, unsigned long base 10 out. Also, the error handling leaves much to be desired.

The final possibility I have found is to use sscanf.

char *myStr; // Initalized to some value somehow.
unsigned long n = 0;
if(sscanf(myStr, "%lu", n) != 1) {
    //do some error handling
}

Again, error handling leaves much to be desired, and a little more complicated than I’d like.

The remaining obvious option is to write my own either a wrapper around one of the previous possibilities or some thing which cycles through the string and manually converts each digit until it reaches ULONG_MAX.

My question is, what are the other options that my google-fu has failed to find? Any thing in the C++ std library that will cleanly convert a string to an unsigned long and throw exceptions on failure?

My apologies if this is a dupe, but I couldn’t find any questions that exactly matched mine.

Answer 1

One way to do it:

stringstream(str) >> ulongVariable;