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clearing a stringstream, impossible?

Started by peter_b Aug 16, 2006 at 3:27 AM 6 replies 1.5k views

Original Post

Aug 16, 2006 at 3:27 AM

Sometimes i use stringstreams for various things. However, i have never been able to reuse a stringstream for several operations. This is because iv never been able to "clear" the old junk out of the stream. stringstream::clear() simply does just not work! It seems it does nothing. Anyone know what im doing wrong? std::stringstream ss; int value = 359; ss<<value; std::string str; str = ss.str(); // this far, all is good, str = "359" // now check this out: ss.clear() // should clear ss, no? it does not. int value2 = 111; ss<<value2; std::string str2; str2 = ss.str(); // now str2 contains "359111", while it should contain just "111" if ".clear()" would actually "clear" the contents of ss.

bubu LV

Aug 16, 2006 at 3:39 AM

Maybe read in manual, what actually clear() method does: http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vclang98/HTML/IOS_basic_iosCCclear.asp#basic_ios::clear

Quote:
void clear(iostate state = goodbit);

The member function replaces the stored stream state information with state | (rdbuf() != 0 ? goodbit : badbit).

It has nothing to do with clearing stream contents.

Basiror

Aug 16, 2006 at 3:39 AM

stringstream ss;

ss.str("");

this will replace the string stored internally with a empty string "".

Basiror

Aug 16, 2006 at 3:42 AM

Quote:
Original post by bubu LV
Maybe read in manual, what actually clear() method does: http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vclang98/HTML/IOS_basic_iosCCclear.asp#basic_ios::clear
Quote:
void clear(iostate state = goodbit);

The member function replaces the stored stream state information with state | (rdbuf() != 0 ? goodbit : badbit).

It has nothing to do with clearing stream contents.

thr clear() function clears the flags only

peter_b

Aug 16, 2006 at 5:40 AM

ah ok, i tought clear() was the same for all std containers.

however Basiror.
If i do this:

std::stringstream ss;
ss.str("");
int id = 359;
ss<std::string value = ss.str();

// then value will contain only "", not "359" =(
// any idea? seems setting the internal string prevents further writing via the << >> operators

Brother Bob

Aug 16, 2006 at 5:57 AM

Quote:
Original post by peter_b
ah ok, i tought clear() was the same for all std containers.

stringstream is not a container.

Quote:
Original post by peter_b
however Basiror.
If i do this:

std::stringstream ss;
ss.str("");
int id = 359;
ss<std::string value = ss.str();

// then value will contain only "", not "359" =(
// any idea? seems setting the internal string prevents further writing via the << >> operators

Works as expected for me.

peter_b

Aug 16, 2006 at 6:13 AM

Quote:
Original post by Brother Bob
Quote:
Original post by peter_b
ah ok, i tought clear() was the same for all std containers.

stringstream is not a container.

Quote:
Original post by peter_b
however Basiror.
If i do this:

std::stringstream ss;
ss.str("");
int id = 359;
ss<std::string value = ss.str();

// then value will contain only "", not "359" =(
// any idea? seems setting the internal string prevents further writing via the << >> operators

Works as expected for me.

Ok it does, posted a simplified sample, my bad. But try this:

std::string value = "359";
std::stringstream ss;
ss<unsigned int id;
ss>>id;
id = id+1;
ss.str("");
ss<value = ss.str();

// value should contain "360", but it dosen't. Atleast not for me =/

Fruny

Aug 16, 2006 at 6:30 AM

That's because you also need to clear the end-of-file flag from the stream. Thus, you need both ss.clear(); and ss.str("");.

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