Assigning a string variable to an unsigned char variable

Question

Assume I have a string s that represents a hex value:

string s="0x80";

I want to assign the value of s to v, where v is defined as:

unsigned char v;

What is the simplest way of doing it?

Why do I need it? Because in here, a bloom filter is represented as a vector of unsigned char where each char represents 8 bits. I want to access each char, perform some computation on it, and then store it back in a compatible form. Also, when I print each element of the vector (which is of type unsigned char) it appears in a hex form, e.g. 3a, 98, etc.

Why are strings involved at all? "vector of unsigned char" is not a string (just use it directly) — user555045
– user555045, Commented Sep 3, 2018 at 18:54
Assuming the number is always going to fit in an unsigned char, v = std::stoul(s, nullptr, 16); Documentation — Shawn
– Shawn, Commented Sep 3, 2018 at 18:55
But it sounds more like you're actually asking how to convert a number to a hex string... or have a fundamental misunderstanding of how numbers are stored in a computer. — Shawn
– Shawn, Commented Sep 3, 2018 at 18:57

R Sahu · Accepted Answer · 2018-09-03 18:53:26Z

5

Construct a std::istringstream from the string.
Extract the number from the istringstream by indicating that the stream contains data in hex format.
Assign the number to a char.

std::string s="0x80";
std::istringstream str(s);
int num;
str >> std::hex >> num;

unsigned char v = num;

answered Sep 3, 2018 at 18:53

R Sahu

207k15 gold badges168 silver badges291 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Alan Birtles Over a year ago

note this will ignore any invalid characters, e.g. "0x8G" will parse successfully

KamilCuk · Accepted Answer · 2018-09-03 18:54:41Z

4

Convert string to integer:

unsigned char num = std::stoi(s, nullptr, 0);

answered Sep 3, 2018 at 18:54

KamilCuk

146k8 gold badges84 silver badges154 bronze badges

1 Comment

Alan Birtles Over a year ago

Shouldn't pass nullptr as the second parameter or the function will silently ignore some errors

Collectives™ on Stack Overflow

Assigning a string variable to an unsigned char variable

2 Answers 2

1 Comment

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related