check the existence of string

[Gary Wessle]

hi

or is there a better way to check the existence of "py" in a string
"s"?

string s = "djrfpyfd";
string t = "py";
string r = s.substr(s.find("py"),2);
cout << (t==r) << endl;

thanks

 

[Victor Bazarov]

or is there a better way to check the existence of "py" in a string
"s"?

string s = "djrfpyfd";
string t = "py";
string r = s.substr(s.find("py"),2);
cout << (t==r) << endl;

'find' returns 'std::string::npos' if the [sub]string is NOT found. So,
if you just wanted to check the existence, you just need to check the
return value of 'find'. There is no need to extract and compare. RTFM

V

 

[Gary Wessle]

or is there a better way to check the existence of "py" in a string
"s"?

string s = "djrfpyfd";
string t = "py";
string r = s.substr(s.find("py"),2);
cout << (t==r) << endl;

'find' returns 'std::string::npos' if the [sub]string is NOT found. So,
if you just wanted to check the existence, you just need to check the
return value of 'find'. There is no need to extract and compare. RTFM

V

the fix:
string s = "djrfpyfd";
string t = "pyd";
if ( (s.find(t,0))!= string::npos )
cout << "found" << endl;

however the next does not work

#include <string>
using std::string;

( (s.find(t,0))!= string::npos ) ? return 2.0 : return 4.0;

I get
: error: expected primary-expression before 'return'
: error: expected `:' before 'return'
: error: expected primary-expression before 'return'
: error: expected `;' before 'return'
: error: expected primary-expression before ':' token
: error: expected `;' before ':' token

 

[Victor Bazarov]

or is there a better way to check the existence of "py" in a string
"s"?

string s = "djrfpyfd";
string t = "py";
string r = s.substr(s.find("py"),2);
cout << (t==r) << endl;

'find' returns 'std::string::npos' if the [sub]string is NOT found.
So, if you just wanted to check the existence, you just need to
check the return value of 'find'. There is no need to extract and
compare. RTFM

V

the fix:
string s = "djrfpyfd";
string t = "pyd";
if ( (s.find(t,0))!= string::npos )
cout << "found" << endl;

however the next does not work

#include <string>
using std::string;

( (s.find(t,0))!= string::npos ) ? return 2.0 : return 4.0;

I get

error: expected primary-expression before 'return'
error: expected `:' before 'return'
error: expected primary-expression before 'return'
error: expected `;' before 'return'
error: expected primary-expression before ':' token
error: expected `;' before ':' token

Well, you're trying to have a statement inside an expression.
You simply cannot do that.. What you probably want is

return s.find(t) != string::npos ? 2.0 : 4.0 ;

V

 

[Gary Wessle]

Gary Wessle wrote:
or is there a better way to check the existence of "py" in a string
"s"?

string s = "djrfpyfd";
string t = "py";
string r = s.substr(s.find("py"),2);
cout << (t==r) << endl;

'find' returns 'std::string::npos' if the [sub]string is NOT found.
So, if you just wanted to check the existence, you just need to
check the return value of 'find'. There is no need to extract and
compare. RTFM

V

the fix:
string s = "djrfpyfd";
string t = "pyd";
if ( (s.find(t,0))!= string::npos )
cout << "found" << endl;

however the next does not work

#include <string>
using std::string;

( (s.find(t,0))!= string::npos ) ? return 2.0 : return 4.0;

I get

error: expected primary-expression before 'return'
error: expected `:' before 'return'
error: expected primary-expression before 'return'
error: expected `;' before 'return'
error: expected primary-expression before ':' token
error: expected `;' before ':' token

Well, you're trying to have a statement inside an expression.
You simply cannot do that.. What you probably want is

return s.find(t) != string::npos ? 2.0 : 4.0 ;

that returns -5.20371e-39

it is only when I do

double y;
(s.find(t,0))!= string::npos ? y=2.0 : y=4.0;
return y;
that it works

 

[Victor Bazarov]

Gary Wessle wrote:
or is there a better way to check the existence of "py" in a
string "s"?

string s = "djrfpyfd";
string t = "py";
string r = s.substr(s.find("py"),2);
cout << (t==r) << endl;

'find' returns 'std::string::npos' if the [sub]string is NOT found.
So, if you just wanted to check the existence, you just need to
check the return value of 'find'. There is no need to extract and
compare. RTFM

V
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the fix:
string s = "djrfpyfd";
string t = "pyd";
if ( (s.find(t,0))!= string::npos )
cout << "found" << endl;

however the next does not work

#include <string>
using std::string;

( (s.find(t,0))!= string::npos ) ? return 2.0 : return 4.0;

I get
error: expected primary-expression before 'return'
error: expected `:' before 'return'
error: expected primary-expression before 'return'
error: expected `;' before 'return'
error: expected primary-expression before ':' token
error: expected `;' before ':' token

Well, you're trying to have a statement inside an expression.
You simply cannot do that.. What you probably want is

return s.find(t) != string::npos ? 2.0 : 4.0 ;

that returns -5.20371e-39
Really?!

it is only when I do

double y;
(s.find(t,0))!= string::npos ? y=2.0 : y=4.0;
return y;
that it works

I think that's covered in the FAQ 5.8.

V