How the int TryParse actually works

Question

I ve looked for int TryParse method implementation  how does it work actually  but I haven t found  I have to know  about a string  whether it s a numeric value  but I don t want to convert it at the this time   So I need only the bool result from int TryParse  So the questions are    Is there any function which can provide only the bool result     and    I d like to know  how the int TryParse actually works  is there a try     catch inside or iterates through the characters of input string

User · Answer

Regex is compiled so for speed create it once and reuse it.
The new takes longer than the IsMatch.
This only checks for all digits.
It does not check for range.
If you need to test range then TryParse is the way to go.

private static Regex regexInt = new Regex("^\\d+$");
static bool CheckReg(string value)
{
    return regexInt.IsMatch(value);
}

User · Answer

Check this simple program to understand int TryParse    class Program        static void Main                 string str    7788           int num1          bool n   int TryParse str  out num1           Console WriteLine num1           Console ReadLine              Output is   7788

User · Answer

We can now in C  7 0 and above write this   if  int TryParse inputString  out             do stuff

User · Answer

If you only need the bool result  just use the return value and ignore the out parameter   bool successfullyParsed   int TryParse str  out ignoreMe   if  successfullyParsed                  Edit  Meanwhile you can also have a look at the original source code   System Int32 TryParse    If i want to know how something is actually implemented  i m using ILSpy to decompile the  NET-code    This is the result      int      lt summary gt Converts the string representation of a number to its 32-bit signed integer equivalent  A return value indicates whether the operation succeeded  lt  summary gt       lt returns gt true if s was converted successfully  otherwise  false  lt  returns gt       lt param name  s  gt A string containing a number to convert   lt  param gt       lt param name  result  gt When this method returns  contains the 32-bit signed integer value equivalent to the number contained in s  if the conversion succeeded  or zero if the conversion failed  The conversion fails if the s parameter is null  is not of the correct format  or represents a number less than  lt see cref  F System Int32 MinValue  gt  lt  see gt  or greater than  lt see cref  F System Int32 MaxValue  gt  lt  see gt   This parameter is passed uninitialized   lt  param gt       lt filterpriority gt 1 lt  filterpriority gt  public static bool TryParse string s  out int result        return Number TryParseInt32 s  NumberStyles Integer  NumberFormatInfo CurrentInfo  out result          System Number internal unsafe static bool TryParseInt32 string s  NumberStyles style  NumberFormatInfo info  out int result        byte  stackBuffer   stackalloc byte 1   114   1       Number NumberBuffer numberBuffer   new Number NumberBuffer stackBuffer       result   0      if   Number TryStringToNumber s  style  ref numberBuffer  info  false                 return false            if   style  amp  NumberStyles AllowHexSpecifier     NumberStyles None                if   Number HexNumberToInt32 ref numberBuffer  ref result                         return false                      else               if   Number NumberToInt32 ref numberBuffer  ref result                         return false                      return true      And no  i cannot see any Try-Catchs on the road      System Number private unsafe static bool TryStringToNumber string str  NumberStyles options  ref Number NumberBuffer number  NumberFormatInfo numfmt  bool parseDecimal        if  str    null                return false            fixed  char  ptr   str                char  ptr2   ptr          if   Number ParseNumber ref ptr2  options  ref number  numfmt  parseDecimal       ptr2 - ptr   2    2  lt  str Length  amp  amp   Number TrailingZeros str   ptr2 - ptr   2    2                          return false                      return true        System Number private unsafe static bool ParseNumber ref char  str  NumberStyles options  ref Number NumberBuffer number  NumberFormatInfo numfmt  bool parseDecimal        number scale   0      number sign   false      string text   null      string text2   null      string str2   null      string str3   null      bool flag   false      string str4      string str5      if   options  amp  NumberStyles AllowCurrencySymbol     NumberStyles None                text   numfmt CurrencySymbol          if  numfmt ansiCurrencySymbol    null                        text2   numfmt ansiCurrencySymbol                    str2   numfmt NumberDecimalSeparator          str3   numfmt NumberGroupSeparator          str4   numfmt CurrencyDecimalSeparator          str5   numfmt CurrencyGroupSeparator          flag   true            else               str4   numfmt NumberDecimalSeparator          str5   numfmt NumberGroupSeparator            int num   0      char  ptr   str      char c    ptr      while  true                if   Number IsWhite c      options  amp  NumberStyles AllowLeadingWhite     NumberStyles None      num  amp  1     0  amp  amp    num  amp  1     0      num  amp  32     0  amp  amp  numfmt numberNegativePattern    2                           bool flag2              char  ptr2              if   flag2     options  amp  NumberStyles AllowLeadingSign     NumberStyles None  amp  amp   num  amp  1     0    amp  amp   ptr2   Number MatchChars ptr  numfmt positiveSign      null                                num    1                  ptr   ptr2 -  IntPtr 2   2                            else                               if  flag2  amp  amp   ptr2   Number MatchChars ptr  numfmt negativeSign      null                                        num    1                      number sign   true                      ptr   ptr2 -  IntPtr 2   2                                    else                                       if  c         amp  amp   options  amp  NumberStyles AllowParentheses     NumberStyles None  amp  amp   num  amp  1     0                                                num    3                          number sign   true                                            else                                               if   text    null     ptr2   Number MatchChars ptr  text      null   amp  amp   text2    null     ptr2   Number MatchChars ptr  text2      null                                                         break                                                    num    32                          text   null                          text2   null                          ptr   ptr2 -  IntPtr 2   2                                                                          c     ptr     IntPtr 2   2             int num2   0      int num3   0      while  true                if   c  gt    0   amp  amp  c  lt    9        options  amp  NumberStyles AllowHexSpecifier     NumberStyles None  amp  amp    c  gt    a   amp  amp  c  lt    f       c  gt    A   amp  amp  c  lt    F                            num    4              if  c     0      num  amp  8     0                                if  num2  lt  50                                        number digits  IntPtr  num2       c                      if  c     0     parseDecimal                                                num3   num2                                                          if   num  amp  16     0                                        number scale                                      num    8                            else                               if   num  amp  16     0                                        number scale--                                                    else                       char  ptr2              if   options  amp  NumberStyles AllowDecimalPoint     NumberStyles None  amp  amp   num  amp  16     0  amp  amp    ptr2   Number MatchChars ptr  str4      null     flag  amp  amp   num  amp  32     0  amp  amp   ptr2   Number MatchChars ptr  str2      null                                  num    16                  ptr   ptr2 -  IntPtr 2   2                            else                               if   options  amp  NumberStyles AllowThousands     NumberStyles None     num  amp  4     0     num  amp  16     0      ptr2   Number MatchChars ptr  str5      null  amp  amp    flag     num  amp  32     0     ptr2   Number MatchChars ptr  str3      null                                          break                                    ptr   ptr2 -  IntPtr 2   2                                  c     ptr     IntPtr 2   2             bool flag3   false      number precision   num3      number digits  IntPtr num3      0       if   num  amp  4     0                if   c     E     c     e    amp  amp   options  amp  NumberStyles AllowExponent     NumberStyles None                        char  ptr3   ptr              c     ptr     IntPtr 2   2               char  ptr2              if   ptr2   Number MatchChars ptr  numfmt positiveSign      null                                c     ptr   ptr2                             else                               if   ptr2   Number MatchChars ptr  numfmt negativeSign      null                                        c     ptr   ptr2                       flag3   true                                              if  c  gt    0   amp  amp  c  lt    9                                 int num4   0                  do                                       num4   num4   10    int  c -  0                        c     ptr     IntPtr 2   2                       if  num4  gt  1000                                                num4   9999                          while  c  gt    0   amp  amp  c  lt    9                                                         c     ptr     IntPtr 2   2                                                                                     while  c  gt    0   amp  amp  c  lt    9                    if  flag3                                        num4   -num4                                    number scale    num4                            else                               ptr   ptr3                  c    ptr                                  while  true                        if   Number IsWhite c      options  amp  NumberStyles AllowTrailingWhite     NumberStyles None                                bool flag2                  char  ptr2                  if   flag2     options  amp  NumberStyles AllowTrailingSign     NumberStyles None  amp  amp   num  amp  1     0    amp  amp   ptr2   Number MatchChars ptr  numfmt positiveSign      null                                        num    1                      ptr   ptr2 -  IntPtr 2   2                                    else                                       if  flag2  amp  amp   ptr2   Number MatchChars ptr  numfmt negativeSign      null                                                num    1                          number sign   true                          ptr   ptr2 -  IntPtr 2   2                                            else                                               if  c         amp  amp   num  amp  2     0                                                        num  amp   -3                                                    else                                                       if   text    null     ptr2   Number MatchChars ptr  text      null   amp  amp   text2    null     ptr2   Number MatchChars ptr  text2      null                                                                 break                                                            text   null                              text2   null                              ptr   ptr2 -  IntPtr 2   2                                                                                              c     ptr     IntPtr 2   2                     if   num  amp  2     0                        if   num  amp  8     0                                if   parseDecimal                                        number scale   0                                    if   num  amp  16     0                                        number sign   false                                              str   ptr              return true                      str   ptr      return false

User · Answer

TryParse is the best way for parse or validate in single line   int nNumber   int TryParse  InputString   out nNumber    nNumber   1    Short description    nNumber will initialize with zero  int TryParse   try parse  InputString  and validate it  if succeed set into nNumber  short if    checking int TryParse   result  that return nNumber or 1 as default value

User · Answer

Just because int TryParse gives you the value doesn t mean you need to keep it  you can quite happily do this   int temp  if  int TryParse inputString  out temp            do stuff     You can ignore temp entirely if you don t need it  If you do need it  then hey  it s waiting for you when you want it   As for the internals  as far as I remember it attempts to read the raw bytes of the string as an int and tests whether the result is valid  or something  it s not as simple as iterating through looking for non-numeric characters

[c#] How the int.TryParse actually works

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