c parse int from string

Question

Possible Duplicate    How to parse a string to an int in C          I have done some research and some people say to use atio and others say it s bad  and I can t get it to work anyways   So I just want to ask flat out  whats the right way to convert a string to a int   string s    10   int i   s        Thanks

User · Answer

You can use boost  lexical cast    include  lt iostream gt   include  lt boost lexical cast hpp gt   int main  int argc  char  argv      std  string s1    10   std  string s2    abc   int i      try           i   boost  lexical cast lt int gt   s1            catch  boost  bad lexical cast  amp  e          std  cout  lt  lt   Exception caught      lt  lt  e what    lt  lt  std  endl           try           i   boost  lexical cast lt int gt   s2            catch  boost  bad lexical cast  amp  e          std  cout  lt  lt   Exception caught      lt  lt  e what    lt  lt  std  endl           return 0

User · Answer

You can use istringstream  string s    quot 10 quot       create an input stream with your string  istringstream is str    int i     use is like an input stream is  gt  gt  i

User · Answer

There is no  quot right way quot   If you want a universal  but suboptimal  solution you can use a boost  lexical cast  A common solution for C   is to use std  ostream and   lt  lt  operator  You can use a stringstream and stringstream  str   method for conversion to string  If you really require a fast mechanism  remember the 20 80 rule  you can look for a  quot dedicated quot  solution like C   String Toolkit Library Best Regards  Marcin

User · Answer

In C  11  use std  stoi as   std  string s    quot 10 quot    int i   std  stoi s    Note that std  stoi will throw exception of type std  invalid argument if the conversion cannot be performed  or std  out of range if the conversion results in overflow i e when the string value is too big for int type   You can use std  stol or std stoll though in case int seems too small for the input string   In C  03 98  any of the following can be used   std  string s    quot 10 quot    int i      approach one  std  istringstream s   gt  gt  i    i is 10 after this     approach two  sscanf s c str     quot  d quot    amp i     i is 10 after this    Note that  the above two approaches would fail for input s    quot 10jh quot   They will return 10 instead of notifying error  So the safe and robust approach is to write your own function that parses the input string  and verify each character to check if it is digit or not  and then work accordingly  Here is one robust implemtation  untested though   int to int char const  s         if   s    NULL     s      0            throw std  invalid argument  quot null or empty string argument quot          bool negate    s 0      -            if    s            s     -                     s        if    s      0           throw std  invalid argument  quot sign character only  quot             int result   0          while  s                           if    s  lt   0      s  gt   9                throw std  invalid argument  quot invalid input string quot                   result   result   10   -   s -  0        assume negative number                  s                    return negate   result   -result    -result is positive       This solution is slightly modified version of my another solution

User · Answer

Some handy quick functions  if you re not using Boost    template lt typename T gt  std  string ToString const T amp  v        std  ostringstream ss      ss  lt  lt  v      return ss str       template lt typename T gt  T FromString const std  string amp  str        std  istringstream ss str       T ret      ss  gt  gt  ret      return ret      Example   int i   FromString lt int gt  s   std  string str   ToString i     Works for any streamable types  floats etc   You ll need to  include  lt sstream gt  and possibly also  include  lt string gt

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