Use of sscanf and sstream

 SscanfIs a runtime function, the prototype is very simple:
IntSscanf (
ConstChar* Buffer,
     ConstChar* Format[,
   Argument]...
);
Its powerful functions are reflected in the support for format and type conversion.

The format can be one or more {% [*] [Width] [{H | L | I64 | L}] Type       |       ' ' |       '\ T' | '\ N' | Non-% symbol },
Note: {A | B | c} indicates A, B, and C. Select [d], which indicates D or D. 
Width: width, which can be ignored. Its usage is as follows:
Const       Char Sourcestr [] = "Hello, World ";
Char Buf [10] = {0 };
Sscanf (sourcestr, "% 5s ", Buf );         // % 5 s, only 5 Characters
Cout < Buf < Endl;
Result: Hello

{H|L|I64|L}: The parameter size. Generally, h indicates the size of a single byte, And I indicates 2 bytes.Size, L indicates 4-byte size (with the exception of double), and l64 indicates 8-byte size.
Type: This is a lot, that is, % s, % d and so on.
Special:

% * [Width][{H|L|I64|L}] Type   It indicates that the values that meet the condition are filtered out and will not be written to the target parameter. For example:
Const   CharSourcestr []="Hello,World ";
CharBuf [10]={0 };
Sscanf (sourcestr,"% * S % s ",Buf );    // % * S indicates that the first matching % s is filtered out, that is, hello is filtered out.
Cout<Buf <Endl;
Result: World

Collection operations are supported:
  % [A-Z]   Match any character from A to Z, greedy (as many as possible)
  % [AB ']Matching A, B, and ', greedy
  % [^ A]Match any character other than a, greedy
For example, if you specify a string iios/12ddwdff @ 122 and obtain the string between/and @, filter out "iios/" first, then, send a string of content other than '@' to the Buf:

Sscanf ("iios/12ddwdff @ 122", "% * [^/]/% [^ @]", Buf );

Printf ("% s \ n", Buf); Result: 12 ddwdff
Sscanf can extract integers, floating-point numbers, and strings from strings. It is easy to use, especially for integers and floating-point numbers.

 StringstreamAs the name suggests, it is the input and output stream of a string, which is similar to fstream.

Header file: # include <sstream>

 

Stringstream is usually used for data conversion. Compared with the C-database conversion, it is more secure, automatic, and direct.

Example 1: Convert the basic data type from int to string
# Include <string>
# Include <sstream>
# Include <iostream>
Int main ()
{
   STD: stringstream stream;
   STD: String result;
   Int I = 1000;
   Stream <I; // input int streams
   Stream> result; // extract the int value inserted earlier from stream
   STD: cout <result <STD: Endl; // print the string "1000"
}
Running result: print the string "1000"

Example 2: In addition to basic type conversion, char * conversion is also supported.
# Include <sstream>
# Include <iostream>
Int main ()
{
   STD: stringstream stream;
   Char result [8];
   Stream <8888; // insert 8888 to stream
   Stream> result; // extract the value from stream to result
   STD: cout <result <STD: Endl; // The screen displays "8888"
}
Screen Display "8888"

Example 3: When performing multiple conversions, you must call the stringstream member function clear ().
# Include <sstream>
# Include <iostream>
Int main ()
{
   STD: stringstream stream;
   Int first, second;
   Stream <"456"; // insert a string
   Stream> first; // convert to int
   STD: cout <first <STD: Endl;
   Stream. Clear (); // You must clear the stream before performing multiple conversions.
   Stream <true; // insert bool Value
   Stream> second; // extract int
   STD: cout <second <STD: Endl;
}
Result of running clear:
456
1
No result for running clear:
456
8800090900

Note the differences between stringstream and sscanf:

 

 If STR [] = "one two three four "; 

 

 If read as follows: Char word [20] [20]; for (I = 0; I <n; I ++) sscanf (STR, "% s ", word [I]); 

 

 Every word [I] you read is the word "one", and stringstream reads the words in sequence. 

 

 The reason is very simple. stringstream is to operate on a fixed string, and there is a pointer inside to mark which to read, and sscanf reads STR from the beginning each time. 

 

 Although it is not recommended to use the input and output streams in C ++ in ACM, the problem of small data size occasionally can greatly improve the speed and accuracy of code writing.