比较两个包含浮点值的字符串

Question

I am given two strings which contain a floating point number. I need to compare them. Can I directly compare the strings using std::string::compare and will this always give correct results? My current approach is to convert the string to float using std::stof , however I would prefer to avoid C++11 library functions.

Answer 1

simply comparing strings won't help you in cases like

a = "0.43"
b = "0.4300"

if you need to compare first parse them into float and then compare them

std::string  s1  = "0.6"
std::wstring s2 = "0.7"
float d1  = std::stof(s1);
float d2 = std::stof(s2);

and then compare them

here is a full program

#include <iostream>   // std::cout
#include <string>     // std::string, std::stof

int main ()
{
  std::string  s1  = "0.6"
  std::wstring s2 = "0.7"
  float d1  = std::stof(s1);
  float d2 = std::stof(s2);

  if(d1 == d2)
     std::cout << "Equals!";
  else
     std::cout << "Not Equals!";
  return 0;
}

click here for more reading on stof

Answer 2

What about writing some ugly codes? It may not be good practice but ...

int compare (const string &str1, const string &str2) {
    string *s1 = &str1, *s2 = &str2;
    int isReverse = 1;
    int len1, len2;

    if (str1.length() > str2.length()) {
        s1 = &str2;
        s2 = &str1;
        isReverse = -1;
    }

    len1 = s1->length();
    len2 = s2->length();

    if (!len1) {
        if (!len2))
            return 0;
        else if ((*s2)[0] != '-')
            return 1*isReverse;
        return -1*isReverse;
    }

    int i = 0;
    while(i < len1) {
        if ((*s1)[i] > (*s2)[i])
            return 1*isReverse;
        else if ((*s1)[i] < (*s2)[i])
            return -1*isReverse;
        i++;
    }

    while (i < len2) {
        if ((*s2)[i] != '0')
            return -1*isReverse;

        i++;
    }

    return 0;
}