CODEWITHSUNDEEP
c++c++11
abhimanyuaryan
abhimanyuaryan

Reputation: 4024

no suitable conversion from std::string to int

I was trying to use some of the function of standard C library but I got this error: no suitable conversion from std::string to int. I have just stepped into learning C++ from C. Please don't over explain this thing with difficult terms. 

#include <iostream>
#include <string> 
#include <cctype>

using namespace std; 

int main(void)
{
  string s1{ "Hello" }; 
  bool what{ isalnum(s1) }; 
  return 0; 
}

Upvotes: 0

Views: 3351

Answers (2)

Mgetz
Mgetz

Reputation: 5138

I'm posting this so that the C++ way of doing this is also here. I prefer this way as it has less dependency on global state

std::locale locale; // grab the current global locale locally, may lock
bool what = true;
for (auto ch : s1) {
    if (!std::isalnum(ch, locale)) {
        what = false;
        break;
    }
}

and the algorithm way:

#include <algorithm>
#include <locale>
#include <functional>

std::locale locale; // grab the current global locale locally, may lock
auto isalnum = std::bind(std::isalnum<char>, std::placeholders::_1, locale);
bool what = std::all_of(s1.begin(), s1.end(), isalnum);

Note: you have to specialize the std::isalnum template to char because otherwise std::bind has no idea what it's binding too.

Upvotes: 0

Mike Seymour
Mike Seymour

Reputation: 254581

isalnum tells you whether a single character, not a whole string, is an alphanumeric.

If you want to check whether the string is alphanumeric, you'll need to look at each character, either with a loop:

bool what = true;
for (unsigned char ch : s1) {
    if (!std::isalnum(ch)) {
        what = false;
        break;
    }
}

or an algorithm:

#include <algorithm>

bool what = std::all_of(s1.begin(), s1.end(), 
    [](unsigned char ch){return std::isalnum(ch);});

As mentioned in the comments, there are many complications and deathtraps when using character classification functions, even though they appear to do something simple. I think my examples avoid most of them, but tread carefully.

Upvotes: 5

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