What exactly does stringstream do

Question

I am trying to learn C   since yesterday and I am using this document http   www cplusplus com files tutorial pdf  page 32    I found a code in the document and I ran it  I tried inputting Rs 5 5 for price and an integer for quantity and the output was 0  I tried inputting 5 5 and 6 and the output was correct      stringstreams  include  lt iostream gt    include  lt string gt    include  lt sstream gt    using namespace std    int main          string mystr     float price   0     int quantity   0      cout  lt  lt   Enter price        getline  cin mystr      stringstream mystr   gt  gt  price     cout  lt  lt   Enter quantity        getline  cin mystr      stringstream mystr   gt  gt  quantity     cout  lt  lt   Total price     lt  lt  price quantity  lt  lt  endl     return 0       Question  What exactly does the mystring command do  Quoting from the document        In this example  we acquire numeric values from the standard input   indirectly  Instead of extracting numeric values  directly from the   standard input  we get lines from the standard input  cin  into a   string object  mystr   and then  we extract the integer values from   this string into a variable of type int  quantity      My impression was that the function will take the integral part of a string and use that as input    I don t exactly know how to ask a question here  I am also new to programming  Thank you

User · Accepted Answer

Sometimes it is very convenient to use stringstream to convert between strings and other numerical types. The usage of stringstream is similar to the usage of iostream, so it is not a burden to learn.

Stringstreams can be used to both read strings and write data into strings. It mainly functions with a string buffer, but without a real I/O channel.

The basic member functions of stringstream class are

str(), which returns the contents of its buffer in string type.
str(string), which set the contents of the buffer to the string argument.

Here is an example of how to use string streams.

ostringstream os;
os << "dec: " << 15 << " hex: " << std::hex << 15 << endl;
cout << os.str() << endl;

The result is dec: 15 hex: f.

istringstream is of more or less the same usage.

To summarize, stringstream is a convenient way to manipulate strings like an independent I/O device.

FYI, the inheritance relationships between the classes are:

string stream classes

User · Answer

You entered an alphanumeric and int  blank delimited in mystr   You then tried to convert the first token  blank delimited  into an int   The first token was RS which failed to convert to int  leaving a zero for myprice  and we all know what zero times anything yields   When you only entered int values the second time  everything worked as you expected    It was the spurious RS that caused your code to fail

User · Answer

From C   Primer      The istringstream type reads a string  ostringstream writes a string  and stringstream reads and writes the string    I come across some cases where it is both convenient and concise to use stringstream   case 1  It is from one of the solutions for this leetcode problem  It demonstrates a very suitable case where the use of stringstream is efficient and concise   Suppose a and b are complex numbers expressed in string format  we want to get the result of multiplication of a and b also in string format  The code is as follows   string a    1 2i   b    1 3i   istringstream sa a   sb b   ostringstream out   int ra  ia  rb  ib  char buff     only read integer values to get the real and imaginary part of     of the original complex number sa  gt  gt  ra  gt  gt  buff  gt  gt  ia  gt  gt  buff  sb  gt  gt  rb  gt  gt  buff  gt  gt  ib  gt  gt  buff   out  lt  lt  ra rb-ia ib  lt  lt       lt  lt  ra ib ia rb  lt  lt   i       final result in string format string result   out str      case 2  It is also from a leetcode problem that requires you to simplify the given path string  one of the solutions using stringstream is the most elegant that I have seen   string simplifyPath string path        string res  tmp      vector lt string gt  stk      stringstream ss path       while getline ss tmp                 if  tmp       or tmp         continue          if  tmp         and  stk empty    stk pop back            else if  tmp          stk push back tmp             for auto str   stk  res        str      return res empty           res        Without the use of stringstream  it would be difficult to write such concise code

User · Answer

To answer the question  stringstream basically allows you to treat a string object like a stream  and use all stream functions and operators on it   I saw it used mainly for the formatted output input goodness   One good example would be c   implementation of converting number to stream object   Possible example   template  lt class T gt  string num2str const T amp  num  unsigned int prec   12        string ret      stringstream ss      ios base  fmtflags ff   ss flags        ff    ios base  floatfield      ff    ios base  fixed      ss flags ff       ss precision prec       ss  lt  lt  num      ret   ss str        return ret       Maybe it s a bit complicated but it is quite complex  You create stringstream object ss  modify its flags  put a number into it with operator lt  lt   and extract it via str    I guess that operator gt  gt  could be used   Also in this example the string buffer is hidden and not used explicitly  But it would be too long of a post to write about every possible aspect and use-case   Note  I probably stole it from someone on SO and refined  but I don t have original author noted

[c++] What exactly does stringstream do?

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