How can I pad an int with leading zeros when using cout operator

Question

I want cout to output an int with leading zeros  so the value 1 would be printed as 001 and the value 25 printed as 025  How can I do this

User · Answer

In C  20 you ll be able to do  std  cout  lt  lt  std  format  quot   03  quot   25      prints 025  In the meantime you can use the  fmt  library  std  format is based on  Disclaimer  I m the author of  fmt  and C  20 std  format

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Another example to output date and time using zero as a fill character on instances of single digit values   2017-06-04 18 13 02   include  stdafx h   include  lt iostream gt   include  lt iomanip gt   include  lt ctime gt  using namespace std   int main         time t t   time 0        Get time now     struct tm   now   localtime  amp t       cout fill  0        cout  lt  lt   now- gt tm year   1900   lt  lt   -           lt  lt  setw 2   lt  lt   now- gt tm mon   1   lt  lt   -           lt  lt  setw 2   lt  lt  now- gt tm mday  lt  lt               lt  lt  setw 2   lt  lt  now- gt tm hour  lt  lt               lt  lt  setw 2   lt  lt  now- gt tm min  lt  lt               lt  lt  setw 2   lt  lt  now- gt tm sec          lt  lt  endl      return 0

User · Answer

With the following    include  lt iomanip gt   include  lt iostream gt   int main         std  cout  lt  lt  std  setfill  0    lt  lt  std  setw 5   lt  lt  25      the output will be  00025   setfill is set to the space character       by default  setw sets the width of the field to be printed  and that s it     If you are interested in knowing how the to format output streams in general  I wrote an answer for another question  hope it is useful  Formatting C   Console Output

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Another way to achieve this is using old printf   function of C language  You can use this like  int dd   1  mm   9  yy   1  printf   02d -  02d -  04d   mm  dd  yy     This will print 09 - 01 - 0001 on the console   You can also use another function sprintf   to write formatted output to a string like below   int dd   1  mm   9  yy   1  char s 25   sprintf s    02d -  02d -  04d   mm  dd  yy   cout  lt  lt  s    Don t forget to include stdio h header file in your program for both of these functions  Thing to be noted   You can fill blank space either by 0 or by another char  not number   If you do write something like  24d format specifier than this will not fill 2 in blank spaces  This will set pad to 24 and will fill blank spaces

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cout fill       cout  lt  lt  -12345  lt  lt  endl     print default value with no field width cout  lt  lt  setw 10   lt  lt  -12345  lt  lt  endl     print default with field width cout  lt  lt  setw 10   lt  lt  left  lt  lt  -12345  lt  lt  endl     print left justified cout  lt  lt  setw 10   lt  lt  right  lt  lt  -12345  lt  lt  endl     print right justified cout  lt  lt  setw 10   lt  lt  internal  lt  lt  -12345  lt  lt  endl     print internally justified   This produces the output   -12345     -12345 -12345         -12345 -    12345

User · Answer

I would use the following function  I don t like sprintf  it doesn t do what I want     define hexchar x         x  amp 0x0F  gt 9    x   A -10    x   0    typedef signed long long   Int64      Special printf for numbers only    See formatting information below           Print the number  n  in the given  base        using exactly  numDigits         Print   - if signed flag  isSigned  is TRUE        Use the character specified in  padchar  to pad extra characters           Examples        sprintfNum pszBuffer  6  10  6   TRUE         1234    -- gt      1234        sprintfNum pszBuffer  6  10  6  FALSE   0     1234    -- gt    001234        sprintfNum pszBuffer  6  16  6  FALSE       0x5AA5    -- gt      5AA5  void sprintfNum char  pszBuffer  int size  char base  char numDigits  char isSigned  char padchar  Int64 n        char  ptr   pszBuffer       if   pszBuffer                return             char  p  buf 32       unsigned long long x      unsigned char count          Prepare negative number     if  isSigned  amp  amp   n  lt  0                 x   -n            else               x   n                Set up small string buffer     count    numDigits-1  -  isSigned 1 0       p   buf   sizeof  buf        --p     0           Force calculation of first digit         to prevent zero from not printing at all          --p    char hexchar x base       x   x   base          Calculate remaining digits     while count--                if x    0                           Calculate next digit              --p    char hexchar x base               x    base                    else                          No more digits left  pad out to desired length              --p   padchar                          Apply signed notation if requested     if  isSigned                if  n  lt  0                         --p    -                     else if  n  gt  0                         --p                          else                        --p                                Print the string right-justified     count   numDigits      while  count--                 ptr      p              return

User · Answer

cout fill   0         cout width  3    cout  lt  lt  value

[c++] How can I pad an int with leading zeros when using cout << operator?

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