How can I concatenate float with string?

Question

I tried this:

ostringstream myString;
float x;
string s;
if(x)
  myString<<x;
else
  myString<<s;
return myString.str();

But it doesn't work. My goal is to concatenate into myString, a float and a string, with a space between them, before testing if one of them is NULL.

The `if` statement chooses between adding `x` and adding `s`. — Peter Wood, Mar 13 '13 at 12:30
While not a `float` the same techniques can be used: http://stackoverflow.com/questions/10516196/append-an-int-to-a-stdstring/10516313#10516313 — hmjd, Mar 13 '13 at 12:31
Create a minimal example, 10 lines of code, which compiles and crashes. Post that so we can try it. — Peter Wood, Mar 13 '13 at 12:42

bash.d · Accepted Answer · 2013-03-13T12:51:57.060

3

Why the else inbetween? Try this:

ostringstream myString;
float x;
string s;
if (fabsf(x) > 1e-30){
    myString<<x << " ";
}
if(s.length() > 0)
   myString<<s;
return myString.str(); //does ostringstream has a str()-member?

edited Mar 13 '13 at 12:51

answered Mar 13 '13 at 12:30

bash.d

13,029
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i want to check if one of them is NULL – user2116010 Mar 13 '13 at 12:31
@user2116010 What do you mean by `NULL`? Equal to `0`? Of length zero? – Peter Wood Mar 13 '13 at 12:32
1

x can't be `NULL`, at most `0.0f`. And s can't be `NULL`, either as it is on the stack. – bash.d Mar 13 '13 at 12:32
`ostringstream` has a [`str`](http://en.cppreference.com/w/cpp/io/basic_stringstream/str) member, returning a `string` which has a `c_str` member. – Peter Wood Mar 13 '13 at 12:34
I don't know if it's right but at one point i just make s = NULL and now i want to test if it's null or not – user2116010 Mar 13 '13 at 12:35
@user2116010 `s = NULL` will set `s` to be [`empty`](http://en.cppreference.com/w/cpp/string/basic_string/empty), but not NULL. – Peter Wood Mar 13 '13 at 12:39
beware, floats should never be compared against absolute value. If that is returned from some operation, it might be almost zero, but non-zero. You might try if (fabsf(x) > 1e-30) instead of if (x). Note that std::string(NULL) will crash, so you have to check NULL before it is passed std::string. Use myString.empty() if does not matter. – Pihhan Mar 13 '13 at 12:48

score 2 · Answer 2 · answered Jun 18 '15 at 13:50

C++11 is out. Visual Studio has good support for it, and now has std::to_string(float). After converting to string, just concatenate with the + operator;

string a = "test";
float b = 3.14f;
string result = a + std::to_string(b);

http://en.cppreference.com/w/cpp/string/basic_string/to_string

Also, you might be pleased to now the sto_ family of global functions exist, for converting from string back to a numeral type: http://en.cppreference.com/w/cpp/string/basic_string/stol

score 0 · Answer 3 · answered Mar 13 '13 at 12:31

0

This should do it

ostringstream myString;
float x;
string s;
if ( x != 0)
  myString << x;
myString << " " << s;
return myString.str();

answered Mar 13 '13 at 12:31

Ed Rowlett-Barbu

1,611
10
27

score 0 · Answer 4 · answered Mar 13 '13 at 12:31

0

ostringstream myString;
float x;
string s;
myString<<x << " " <<s;
return myString.str();

answered Mar 13 '13 at 12:31

kassak

3,974
1
25
36

score 0 · Answer 5 · answered Mar 14 '13 at 15:34

0

or use boost::lexical_cast:

return boost::lexical_cast<string>(x) + " " + s;

answered Mar 14 '13 at 15:34

c-urchin

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How can I concatenate float with string?

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