Convert float to std string in C

Question

I have a float value that needs to be put into a std  string  How do I convert from float to string   float val   2 5  std  string my val   val     error here

User · Answer

You can define a template which will work not only just with doubles, but with other types as well.

template <typename T> string tostr(const T& t) { 
   ostringstream os; 
   os<<t; 
   return os.str(); 
}

Then you can use it for other types.

double x = 14.4;
int y = 21;

string sx = tostr(x);
string sy = tostr(y);

User · Answer

This tutorial gives a simple  yet elegant  solution  which i transcribe    include  lt sstream gt   include  lt string gt   include  lt stdexcept gt   class BadConversion   public std  runtime error   public    BadConversion std  string const amp  s        std  runtime error s              inline std  string stringify double x      std  ostringstream o    if    o  lt  lt  x       throw BadConversion  stringify double       return o str          std  string my val   stringify val

User · Answer

Unless you re worried about performance  use string streams    include  lt sstream gt        std  ostringstream ss  ss  lt  lt  myFloat  std  string s ss str       If you re okay with Boost  lexical cast lt   is a convenient alternative   std  string s   boost  lexical cast lt std  string gt  myFloat     Efficient alternatives are e g  FastFormat or simply the C-style functions

User · Answer

If you re worried about performance  check out the Boost  lexical cast library

User · Answer

As of C  11  the standard C   library provides the function std  to string arg  with various supported types for arg

User · Answer

You can use std  to string in C  11  float val   2 5  std  string my val   std  to string val

User · Answer

Use std  to chars once your standard library provides it   std  array lt char  32 gt  buf  auto result   std  to chars buf data    buf data     buf size    val   if  result ec    std  errc        auto str   std  string buf data    result ptr - buf data          use the string   else        handle the error     The advantages of this method are    It is locale-independent  preventing bugs when writing data into formats such as JSON that require     as a decimal point It provides shortest decimal representation with round trip guarantees It is potentially more efficient than other standard methods because it doesn t use the locale and doesn t require allocation   Unfortunately std  to string is of limited utility with floating point because it uses the fixed representation  rounding small values to zero and producing long strings for large values  e g   auto s1   std  to string 1e 40      s1    10000000000000000303786028427003666890752 000000  auto s2   std  to string 1e-40      s2    0 000000   C  20 might get a more convenient std  format API with the same benefits as std  to chars if the P0645 standards proposal gets approved

User · Answer

Important  Read the note at the end   Quick answer   Use to string     available since c  11  example        include  lt iostream gt      include  lt string gt     using namespace std  int main          string pi    pi is     to string 3 1415926       cout lt  lt   pi     lt  lt  pi  lt  lt  endl     return 0      run it yourself   http   ideone com 7ejfaU These are available as well     string to string  int val   string to string  long val   string to string  long long val   string to string  unsigned val   string to string  unsigned long val   string to string  unsigned long long val   string to string  float val   string to string  double val   string to string  long double val     Important Note  As  Michael Konecn   rightfully pointed out  using to string   is risky at best that is its very likely to cause unexpected results  From http   en cppreference com w cpp string basic string to string           With floating point types std  to string may yield unexpected results as the number of significant digits in the returned string can be zero  see the example    The return value may differ significantly from what std  cout prints by default  see the example        std  to string relies on the current locale for formatting purposes  and therefore concurrent calls to std  to string from   multiple threads may result in partial serialization of calls  C  17   provides std  to chars as a higher-performance locale-independent   alternative    The best way would be to use stringstream as others such as  dcp demonstrated in his answer    This issue is demonstrated in the following example   run the example yourself   https   www jdoodle com embed v0 T4k    include  lt iostream gt   include  lt sstream gt   include  lt string gt   template  lt  typename Type  gt  std  string to str  const Type  amp  t      std  ostringstream os    os  lt  lt  t    return os str        int main            more info   https   en cppreference com w cpp string basic string to string   double    f   23 43    double    f2   1e-9    double    f3   1e40    double    f4   1e-40    double    f5   123456789    std  string f str   std  to string  f     std  string f str2   std  to string  f2      Note  returns  0 000000    std  string f str3   std  to string  f3      Note  Does not return  1e 40     std  string f str4   std  to string  f4      Note  returns  0 000000    std  string f str5   std  to string  f5      std  cout  lt  lt   std  cout     lt  lt  f  lt  lt    n       lt  lt   to string     lt  lt  f str  lt  lt    n       lt  lt   ostringstream     lt  lt  to str  f   lt  lt    n n       lt  lt   std  cout     lt  lt  f2  lt  lt    n       lt  lt   to string     lt  lt  f str2  lt  lt    n       lt  lt   ostringstream     lt  lt  to str  f2   lt  lt    n n       lt  lt   std  cout     lt  lt  f3  lt  lt    n       lt  lt   to string     lt  lt  f str3  lt  lt    n       lt  lt   ostringstream     lt  lt  to str  f3   lt  lt    n n       lt  lt   std  cout     lt  lt  f4  lt  lt    n       lt  lt   to string     lt  lt  f str4  lt  lt    n       lt  lt   ostringstream     lt  lt  to str  f4   lt  lt    n n       lt  lt   std  cout     lt  lt  f5  lt  lt    n       lt  lt   to string     lt  lt  f str5  lt  lt    n       lt  lt   ostringstream     lt  lt  to str  f5   lt  lt    n      return 0      output     std  cout  23 43 to string  23 430000 ostringstream  23 43  std  cout  1e-09 to string  0 000000 ostringstream  1e-09  std  cout  1e 40 to string  10000000000000000303786028427003666890752 000000 ostringstream  1e 40  std  cout  1e-40 to string  0 000000 ostringstream  1e-40  std  cout  1 23457e 08 to string  123456789 000000 ostringstream  1 23457e 08

[c++] Convert float to std::string in C++

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