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      std::printf,std::fprintf,std::sprintf,std::snprintf

      From cppreference.com
      <cpp‎ |io‎ |c
       
       
       
       
      Defined in header<cstdio>
      int printf(constchar* format, ...);
      		 (1)
      int fprintf(std::FILE* stream,constchar* format, ...);
      		 (2)
      int sprintf(char* buffer,constchar* format, ...);
      		 (3)
      int snprintf(char* buffer,std::size_t buf_size,constchar* format, ...);
      		 (4)(since C++11)

      Loads the data from the given locations, converts them to character string equivalents and writes the results to a variety of sinks.

      1) Writes the results tostdout.
      2) Writes the results to a file streamstream.
      3) Writes the results to a character stringbuffer.
      4) Writes the results to a character stringbuffer. At mostbuf_size-1 characters are written. The resulting character string will be terminated with a null character, unlessbuf_size is zero. Ifbuf_size is zero, nothing is written andbuffer may be a null pointer, however the return value (number of bytes that would be written not including the null terminator) is still calculated and returned.

      If a call tosprintf orsnprintf causes copying to take place between objects that overlap, the behavior is undefined (e.g.sprintf(buf,"%s text", buf);).

      Contents

      [edit]Parameters

      stream - output file stream to write to
      buffer - pointer to a character string to write to
      buf_size - up tobuf_size-1 characters may be written, plus the null terminator
      format - pointer to a null-terminated multibyte string specifying how to interpret the data
      ... - arguments specifying data to print. If any argument afterdefault argument promotions is not the type expected by the corresponding conversion specification (the expected type is the promoted type or a compatible type of the promoted type), or if there are fewer arguments than required byformat, the behavior is undefined. If there are more arguments than required byformat, the extraneous arguments are evaluated and ignored

      Theformat string consists of ordinary byte characters (except%), which are copied unchanged into the output stream, and conversion specifications. Each conversion specification has the following format:

      • introductory% character.
      • (optional) one or more flags that modify the behavior of the conversion:
      • -: the result of the conversion is left-justified within the field (by default it is right-justified).
      • +: the sign of signed conversions is always prepended to the result of the conversion (by default the result is preceded by minus only when it is negative).
      • space: if the result of a signed conversion does not start with a sign character, or is empty, space is prepended to the result. It is ignored if+ flag is present.
      • #:alternative form of the conversion is performed. See the table below for exact effects otherwise the behavior is undefined.
      • 0: for integer and floating-point number conversions, leading zeros are used to pad the field instead ofspace characters. For integer numbers it is ignored if the precision is explicitly specified. For other conversions using this flag results in undefined behavior. It is ignored if- flag is present.
      • (optional) integer value or* that specifies minimum field width. The result is padded withspace characters (by default), if required, on the left when right-justified, or on the right if left-justified. In the case when* is used, the width is specified by an additional argument of typeint, which appears before the argument to be converted and the argument supplying precision if one is supplied. If the value of the argument is negative, it results with the- flag specified and positive field width (Note: This is the minimum width: The value is never truncated.).
      • (optional). followed by integer number or*, or neither that specifiesprecision of the conversion. In the case when* is used, theprecision is specified by an additional argument of typeint, which appears before the argument to be converted, but after the argument supplying minimum field width if one is supplied. If the value of this argument is negative, it is ignored. If neither a number nor* is used, the precision is taken as zero. See the table below for exact effects ofprecision.
      • (optional)length modifier that specifies the size of the argument (in combination with the conversion format specifier, it specifies the type of the corresponding argument).
      • conversion format specifier.

      The following format specifiers are available:

      Conversion
      Specifier      		ExplanationExpected
      Argument Type
      Length Modifier→hhhnonellljztL
      Only available since C++11→YesYesYesYesYes
      %Writes literal%. The full conversion specification must be%%.N/AN/AN/AN/AN/AN/AN/AN/AN/A
      c

      Writes asingle character.

      • The argument is first converted tounsignedchar.
      • If thel modifier is used, the argument is first converted to a character string as if by%ls with awchar_t[2] argument.
      		N/AN/A
      int
      std::wint_t
      		N/AN/AN/AN/AN/A
      s

      Writes acharacter string.

      • The argument must be a pointer to the initial element of an array of characters.
      • Precision specifies the maximum number of bytes to be written. IfPrecision is not specified, writes every byte up to and not including the first null terminator.
      • If thel specifier is used, the argument must be a pointer to the initial element of an array ofwchar_t, which is converted to char array as if by a call tostd::wcrtomb with zero-initialized conversion state.
      		N/AN/A
      char*
      wchar_t*
      		N/AN/AN/AN/AN/A
      d
      i

      Converts asigned integer into decimal representation[-]dddd.

      • Precision specifies the minimum number of digits to appear. The default precision is1.
      • If both the converted value and the precision are​0​ the conversion results in no characters.
      • For thez modifier, the expected argument type is the signed version ofstd::size_t.
      signedchar
      short
      int
      long
      longlong
      ※
      		N/A
      o

      Converts anunsigned integer into octal representationoooo.

      • Precision specifies the minimum number of digits to appear. The default precision is1.
      • If both the converted value and the precision are​0​ the conversion results in no characters.
      • In thealternative implementation precision is increased if necessary, to write one leading zero. In that case if both the converted value and the precision are​0​, single​0​ is written.
      unsignedchar
      unsignedshort
      unsignedint
      unsignedlong
      unsignedlonglong
      unsigned version ofstd::ptrdiff_t
      		N/A
      x
      X

      Converts anunsigned integer into hexadecimal representationhhhh.

      • For thex conversion lettersabcdef are used.
      • For theX conversion lettersABCDEF are used.
      • Precision specifies the minimum number of digits to appear. The default precision is1.
      • If both the converted value and the precision are​0​ the conversion results in no characters.
      • In thealternative implementation0x or0X is prefixed to results if the converted value is nonzero.
      		N/A
      u

      Converts anunsigned integer into decimal representationdddd.

      • Precision specifies the minimum number of digits to appear.
      • The default precision is1.
      • If both the converted value and the precision are​0​ the conversion results in no characters.
      		N/A
      f
      F (C++11)

      Convertsfloating-point number to the decimal notation in the style[-]ddd.ddd.

      • Precision specifies the exact number of digits to appear after the decimal point character.
      • The default precision is6.
      • In thealternative implementation decimal point character is written even if no digits follow it.
      • For infinity and not-a-number conversion style seenotes.
      		N/AN/A
      double
      double(C++11)
      		N/AN/AN/AN/A
      longdouble
      e
      E

      Convertsfloating-point number to the decimal exponent notation.

      • For thee conversion style[-]d.ddd e±dd is used.
      • For theE conversion style[-]d.ddd E±dd is used.
      • The exponent contains at least two digits, more digits are used only if necessary.
      • If the value is​0​, the exponent is also​0​.
      • Precision specifies the exact number of digits to appear after the decimal point character.
      • The default precision is6.
      • In thealternative implementation decimal point character is written even if no digits follow it.
      • For infinity and not-a-number conversion style seenotes.
      		N/AN/AN/AN/AN/AN/A
      a
      A

      (C++11)

      Convertsfloating-point number to the hexadecimal exponent notation.

      • For thea conversion style[-] 0xh.hhh p±d is used.
      • For theA conversion style[-] 0Xh.hhh P±d is used.
      • The first hexadecimal digit is not0 if the argument is a normalized floating-point value.
      • If the value is​0​, the exponent is also​0​.
      • Precision specifies the exact number of digits to appear after the hexadecimal point character.
      • The default precision is sufficient for exact representation of the value.
      • In thealternative implementation decimal point character is written even if no digits follow it.
      • For infinity and not-a-number conversion style seenotes.
      		N/AN/AN/AN/AN/AN/A
      g
      G

      Convertsfloating-point number to decimal or decimal exponent notation depending on the value and theprecision.

      • For theg conversion style conversion with stylee orf will be performed.
      • For theG conversion style conversion with styleE orf(until C++11)F(since C++11) will be performed.
      • LetP equal the precision if nonzero,6 if the precision is not specified, or1 if the precision is​0​. Then, if a conversion with styleE would have an exponent ofX:
        • IfP > X ≥ −4, the conversion is with stylef orF(since C++11) and precisionP − 1 − X.
        • Otherwise, the conversion is with stylee orE and precisionP − 1.
      • Unlessalternative representation is requested the trailing zeros are removed, also the decimal point character is removed if no fractional part is left.
      • For infinity and not-a-number conversion style seenotes.
      		N/AN/AN/AN/AN/AN/A
      n

      Returns thenumber of characters written so far by this call to the function.

      • The result iswritten to the value pointed to by the argument.
      • The specification may not contain anyflag,field width, orprecision.
      • For thez modifier, the expected argument type isS*, whereS is the signed version ofstd::size_t.
      signedchar*
      short*
      int*
      long*
      longlong*
      ※
      		N/A
      p

      Writes an implementation defined character sequence defining apointer.

      		N/AN/A
      void*
      		N/AN/AN/AN/AN/AN/A
      Notes

      The floating-point conversion functions convert infinity toinf orinfinity. Which one is used is implementation defined.

      Not-a-number is converted tonan ornan(char_sequence). Which one is used is implementation defined.

      The conversionsF,E,G,A outputINF,INFINITY,NAN instead.

      The conversion specifier used to printchar,unsignedchar,signedchar,short, andunsignedshort expects promoted types ofdefault argument promotions, but before printing its value will be converted tochar,unsignedchar,signedchar,short, andunsignedshort. It is safe to pass values of these types because of the promotion that takes place when a variadic function is called.

      The correct conversion specifications for the fixed-width character types (std::int8_t, etc) are defined in the header<cinttypes> (althoughPRIdMAX,PRIuMAX, etc is synonymous with%jd,%ju, etc).

      The memory-writing conversion specifier%n is a common target of security exploits where format strings depend on user input.

      There is asequence point after the action of each conversion specifier; this permits storing multiple%n results in the same variable or, as an edge case, printing a string modified by an earlier%n within the same call.

      If a conversion specification is invalid, the behavior is undefined.

      [edit]Return value

      1,2) Number of characters written if successful or a negative value if an error occurred.
      3) Number of characters written if successful (not including the terminating null character) or a negative value if an error occurred.
      4) Number of characters that would have been written for a sufficiently large buffer if successful (not including the terminating null character), or a negative value if an error occurred. Thus, the (null-terminated) output has been completely written if and only if the returned value is nonnegative and less thanbuf_size.

      [edit]Notes

      POSIX specifies thaterrno is set on error. It also specifies additional conversion specifications, most notably support for argument reordering (n$ immediately after% indicatesnth argument).

      Callingstd::snprintf with zerobuf_size and null pointer forbuffer is useful (when the overhead of double-call is acceptable) to determine the necessary buffer size to contain the output:

      auto fmt="sqrt(2) = %f";int sz= std::snprintf(nullptr,0, fmt,std::sqrt(2));std::vector<char> buf(sz+1);// note +1 for null terminatorstd::sprintf(buf.data(), fmt,std::sqrt(2));// certain to fit

      [edit]Example

      Run this code
      #include <cinttypes>#include <cstdint>#include <cstdio>#include <limits> int main(){constchar* s="Hello";    std::printf("Strings:\n");// same as std::puts("Strings:");    std::printf("\t[%10s]\n", s);    std::printf("\t[%-10s]\n", s);    std::printf("\t[%*s]\n",10, s);    std::printf("\t[%-10.*s]\n",4, s);    std::printf("\t[%-*.*s]\n",10,4, s);     std::printf("Characters:\t%c %%\n",'A');     std::printf("Integers:\n");    std::printf("\tDecimal:\t%i %d %.6i %i %.0i %+i %i\n",1,2,3,0,0,4,-4);    std::printf("\tHexadecimal:\t%x %x %X %#x\n",5,10,10,6);    std::printf("\tOctal:\t%o %#o %#o\n",10,10,4);     std::printf("Floating point:\n");    std::printf("\tRounding:\t%f %.0f %.32f\n",1.5,1.5,1.3);    std::printf("\tPadding:\t%05.2f %.2f %5.2f\n",1.5,1.5,1.5);    std::printf("\tScientific:\t%E %e\n",1.5,1.5);    std::printf("\tHexadecimal:\t%a %A\n",1.5,1.5);    std::printf("\tSpecial values:\t0/0=%g 1/0=%g\n",0.0/0.0,1.0/0.0);     std::printf("Variable width control:\n");    std::printf("\tright-justified variable width: '%*c'\n",5,'x');int r= std::printf("\tleft-justified variable width : '%*c'\n",-5,'x');    std::printf("(the last printf printed %d characters)\n", r);     std::printf("Fixed-width types:\n");std::uint32_t val=std::numeric_limits<std::uint32_t>::max();    std::printf("\tLargest 32-bit value is %"PRIu32" or %#"PRIx32"\n",                                                 val,            val);}

      Possible output:

      Strings:[     Hello][Hello     ][     Hello][Hell      ][Hell      ]Characters:A %Integers:Decimal:    1 2 000003 0  +4 -4Hexadecimal:5 a A 0x6Octal:      12 012 04Floating point:Rounding:1.500000 2 1.30000000000000004440892098500626Padding:01.50 1.50  1.50Scientific:1.500000E+00 1.500000e+00Hexadecimal:0x1.8p+0 0X1.8P+0Special values:0/0=-nan 1/0=infVariable width control:right-justified variable width: '    x'left-justified variable width : 'x    '(the last printf printed 41 characters)Fixed-width types:Largest 32-bit value is 4294967295 or 0xffffffff

      [edit]See also

      prints formatted wide character output tostdout, a file stream or a buffer
      (function)[edit]
      prints formatted output tostdout, a file stream or a buffer
      using variable argument list
      (function)[edit]
      writes a character string to a file stream
      (function)[edit]
      reads formatted input fromstdin, a file stream or a buffer
      (function)[edit]
      (C++17)
      		 converts an integer or floating-point value to a character sequence
      (function)[edit]
      (C++23)
      		 prints tostdout or a file stream usingformatted representation of the arguments
      (function template)[edit]
      (C++23)
      		 same asstd::print except that each print is terminated by additional new line
      (function template)[edit]
      C documentation forprintf,fprintf,sprintf,snprintf
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