digit analysis for hashing (asking for peer review)

[weak lynx]

int digit_analysis(const std::string &key, int tableSize)
{
if (keystr.length() < 6)
{
std::cerr << "Key string is too short to extract digits 3 to 6." << std::endl;
return 0;
}

    long long keyValue = std::stoll(key);
    std::string keystr = std::(newValue);


    std::string backwardDigit = keystr.substr(2,4);
    std::reverse(backwardDigit.begin(), backwardDigit.end());
    int hash = std::stoi(backwardDigit);
    return hash % tableSize;
} 

how does this look?

[steel egret]

std::(newValue)?

[weak lynx]

std::(keyValue)

i had it renamed

[steel egret]

what does that do though

;compile cpp long long keyValue=42; std::(KeyValue);

[glad viper]

Compiler Output

<source>: In function 'int main()':
<source>:5:6: error: expected unqualified-id before '(' token
    5 | std::(KeyValue);
      |      ^
<source>:5:7: error: 'KeyValue' was not declared in this scope; did you mean 'keyValue'?
    5 | std::(KeyValue);
      |       ^~~~~~~~
      |       keyValue
Build failed

halalaluyafail3 | c++ | x86-64 gcc 14.2 | godbolt.org

[weak lynx]

turns it back into a string

[steel egret]

so you meant std::to_string?

[weak lynx]

here is my midsquare method.

[weak lynx]

yes that is what i meant. ty

int digit_analysis(const std::string &key, int tableSize)
{
if (keystr.length() < 6)
{
std::cerr << "Key string is too short to extract digits 3 to 6." << std::endl;
return 0; //making sure the value is more than 6 digits
}

    long long keyValue = std::stoll(key); //turning the key into long long
    std::string keystr = std::to_string(keyValue); //same thinf as midsquare method


    std::string backwardDigit = keystr.substr(2,4);
    std::reverse(backwardDigit.begin(), backwardDigit.end()); //reveseing the begining and end of the digits 
    int hash = std::stoi(backwardDigit); //string to int 
    return hash % tableSize;
}

[steel egret]

do negative numbers need to be considered here

[weak lynx]

no i dont believe so

but that can be put into consideration

im hashing using a linked list class that i created

[steel egret]

looks alright, though I would recommend doing integer arithmetic instead of constructing a string and doing substr and reverse

[weak lynx]

like how?

[steel egret]

;compile cpp //assuming size()>5 here std::string key="12345678"; long long keyValue; if(std::from_chars(key.data()+2,key.data()+5,keyValue).ec!=std::errc()){ //handle error } keyValue=keyValue%10*100+keyValue/10%10*10+keyValue/100; std::cout<<keyValue<<'\n';

[glad viper]

Program Output

543

halalaluyafail3 | 51ms | c++ | x86-64 gcc 14.2 | godbolt.org

[steel egret]

something like this I was thinking of

[weak lynx]

ok ill try that

[steel egret]

though if converting to long long and back to string matters then this would be different

[steel egret]

also you're referencing keystr here before you declared it

[weak lynx]

i moved it around. and added your code as comments

i want to let my prof know about the comment code first. just in case. becuse im not too sure what it does

there is also this, which i do not understand

[hidden parcel]

cppreference.com

std::from_chars, std::from_chars_result

std::from_chars_result from_chars(
    const char* first,
    const char* last,
    /*see below*/ &value,
    int base = 10);
// ... and 5 more

Defined in

<charconv>

[weak lynx]

thats for the length dependence?

[weak lynx]

whats this?

[steel egret]

a function