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      printf, fprintf, sprintf, snprintf, printf_s, fprintf_s, sprintf_s, snprintf_s

      From cppreference.com
      <c‎ |io
       
       
      File input/output
      Types and objects
      Functions
      File access
      Unformatted input/output
      (C95)(C95)
      (C95)
      (C95)(C95)
      (C95)
      (C95)

      Formatted input
      Direct input/output
      Formatted output
      printffprintfsprintfsnprintfprintf_sfprintf_ssprintf_ssnprintf_s
      (C99)(C11)(C11)(C11)(C11)
      File positioning
      Error handling
      Operations on files
       
      Defined in header<stdio.h>
      (1)
      int printf(constchar*          format, ...);
      		(until C99)
      int printf(constchar*restrict format, ...);
      		(since C99)
      (2)
      int fprintf(FILE*          stream,constchar*          format, ...);
      		(until C99)
      int fprintf(FILE*restrict stream,constchar*restrict format, ...);
      		(since C99)
      (3)
      int sprintf(char*          buffer,constchar*          format, ...);
      		(until C99)
      int sprintf(char*restrict buffer,constchar*restrict format, ...);
      		(since C99)
      int snprintf(char*restrict buffer,size_t bufsz,
                   constchar*restrict format, ...);
      		 (4)(since C99)
      int printf_s(constchar*restrict format, ...);
      		 (5)(since C11)
      int fprintf_s(FILE*restrict stream,constchar*restrict format, ...);
      		 (6)(since C11)
      int sprintf_s(char*restrict buffer, rsize_t bufsz,
                     constchar*restrict format, ...);
      		 (7)(since C11)
      int snprintf_s(char*restrict buffer, rsize_t bufsz,
                     constchar*restrict format, ...);
      		 (8)(since C11)

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

      1) Writes the results to the output streamstdout.
      2) Writes the results to the output streamstream.
      3) Writes the results to a character stringbuffer. The behavior is undefined if the string to be written (plus the terminating null character) exceeds the size of the array pointed to bybuffer.
      4) Writes the results to a character stringbuffer. At mostbufsz-1 characters are written. The resulting character string will be terminated with a null character, unlessbufsz is zero. Ifbufsz 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.
      5-8) Same as(1-4), except that the following errors are detected at runtime and call the currently installedconstraint handler function:
      • the conversion specifier%n is present informat
      • any of the arguments corresponding to%s is a null pointer
      • stream orformat orbuffer is a null pointer
      • bufsz is zero or greater thanRSIZE_MAX
      • encoding errors occur in any of string and character conversion specifiers
      • (forsprintf_s only), the string to be stored inbuffer (including the trailing null) would exceedbufsz.
      As with all bounds-checked functions,printf_s,fprintf_s,sprintf_s, andsnprintf_s are only guaranteed to be available if__STDC_LIB_EXT1__ is defined by the implementation and if the user defines__STDC_WANT_LIB_EXT1__ to the integer constant1 before including<stdio.h>.

      Contents

      [edit]Parameters

      stream - output file stream to write to
      buffer - pointer to a character string to write to
      bufsz - up tobufsz-1 characters may be written, plus the null terminator
      format - pointer to a null-terminated byte 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 C99→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
      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 towcrtomb 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 ofsize_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 ofptrdiff_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 (C99)

      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(C99)
      		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

      (C99)

      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 C99)F(since C99) 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 C99) 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 ofsize_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 (int8_t, etc) are defined in the header<inttypes.h> (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 and is not supported by the bounds-checkedprintf_s family of functions(since C11).

      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 transmitted to the output stream or negative value if an output error or an encoding error (for string and character conversion specifiers) occurred.
      3) number of characters written tobuffer (not counting the terminating null character), or a negative value if an encoding error (for string and character conversion specifiers) occurred.
      4) number of characters (not including the terminating null character) which would have been written tobuffer ifbufsz was ignored, or a negative value if an encoding error (for string and character conversion specifiers) occurred.
      5,6) number of characters transmitted to the output stream or negative value if an output error, a runtime constraints violation error, or an encoding error occurred.
      7) number of characters written tobuffer, not counting the null character (which is always written as long asbuffer is not a null pointer andbufsz is not zero and not greater thanRSIZE_MAX), or zero on runtime constraint violations, and negative value on encoding errors.
      8) number of characters not including the terminating null character (which is always written as long asbuffer is not a null pointer andbufsz is not zero and not greater thanRSIZE_MAX), which would have been written tobuffer ifbufsz was ignored, or a negative value if a runtime constraints violation or an encoding error occurred.

      [edit]Notes

      The C standard andPOSIX specify that the behavior ofsprintf and its variants is undefined when an argument overlaps with the destination buffer. Example:

      sprintf(dst,"%s and %s", dst, t);// <- broken: undefined behavior

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

      Callingsnprintf with zerobufsz and null pointer forbuffer is useful to determine the necessary buffer size to contain the output:

      constchar fmt[]="sqrt(2) = %f";int sz= snprintf(NULL,0, fmt,sqrt(2));char buf[sz+1];// note +1 for terminating null bytesnprintf(buf,sizeof buf, fmt,sqrt(2));

      snprintf_s, just likesnprintf, but unlikesprintf_s, will truncate the output to fit inbufsz-1.

      [edit]Example

      Run this code
      #include <inttypes.h>#include <stdint.h>#include <stdio.h> int main(void){constchar* s="Hello";    printf("Strings:\n");// same as puts("Strings");    printf(" padding:\n");    printf("\t[%10s]\n", s);    printf("\t[%-10s]\n", s);    printf("\t[%*s]\n",10, s);    printf(" truncating:\n");    printf("\t%.4s\n", s);    printf("\t%.*s\n",3, s);     printf("Characters:\t%c %%\n",'A');     printf("Integers:\n");    printf("\tDecimal:\t%i %d %.6i %i %.0i %+i %i\n",1,2,3,0,0,4,-4);    printf("\tHexadecimal:\t%x %x %X %#x\n",5,10,10,6);    printf("\tOctal:\t\t%o %#o %#o\n",10,10,4);     printf("Floating-point:\n");    printf("\tRounding:\t%f %.0f %.32f\n",1.5,1.5,1.3);    printf("\tPadding:\t%05.2f %.2f %5.2f\n",1.5,1.5,1.5);    printf("\tScientific:\t%E %e\n",1.5,1.5);    printf("\tHexadecimal:\t%a %A\n",1.5,1.5);    printf("\tSpecial values:\t0/0=%g 1/0=%g\n",0.0/0.0,1.0/0.0);     printf("Fixed-width types:\n");    printf("\tLargest 32-bit value is %"PRIu32" or %#"PRIx32"\n",UINT32_MAX,UINT32_MAX);}

      Possible output:

      Strings: padding:        [     Hello]        [Hello     ]        [     Hello] truncating:        Hell        HelCharacters:     A %Integers:        Decimal:        1 2 000003 0  +4 -4        Hexadecimal:    5 a A 0x6        Octal:          12 012 04Floating-point:        Rounding:       1.500000 2 1.30000000000000004440892098500626        Padding:        01.50 1.50  1.50        Scientific:     1.500000E+00 1.500000e+00        Hexadecimal:    0x1.8p+0 0X1.8P+0        Special values: 0/0=-nan 1/0=infFixed-width types:        Largest 32-bit value is 4294967295 or 0xffffffff

      [edit]References

      • C23 standard (ISO/IEC 9899:2024):
      • 7.21.6.1 The fprintf function (p: TBD)
      • 7.21.6.3 The printf function (p: TBD)
      • 7.21.6.5 The snprintf function (p: TBD)
      • 7.21.6.6 The sprintf function (p: TBD)
      • K.3.5.3.1 The fprintf_s function (p: TBD)
      • K.3.5.3.3 The printf_s function (p: TBD)
      • K.3.5.3.5 The snprintf_s function (p: TBD)
      • K.3.5.3.6 The sprintf_s function (p: TBD)
      • C17 standard (ISO/IEC 9899:2018):
      • 7.21.6.1 The fprintf function (p: 225-230)
      • 7.21.6.3 The printf function (p: 236)
      • 7.21.6.5 The snprintf function (p: 237)
      • 7.21.6.6 The sprintf function (p: 237)
      • K.3.5.3.1 The fprintf_s function (p: 430)
      • K.3.5.3.3 The printf_s function (p: 432)
      • K.3.5.3.5 The snprintf_s function (p: 432-433)
      • K.3.5.3.6 The sprintf_s function (p: 433)
      • C11 standard (ISO/IEC 9899:2011):
      • 7.21.6.1 The fprintf function (p: 309-316)
      • 7.21.6.3 The printf function (p: 324)
      • 7.21.6.5 The snprintf function (p: 325)
      • 7.21.6.6 The sprintf function (p: 325-326)
      • K.3.5.3.1 The fprintf_s function (p: 591)
      • K.3.5.3.3 The printf_s function (p: 593-594)
      • K.3.5.3.5 The snprintf_s function (p: 594-595)
      • K.3.5.3.6 The sprintf_s function (p: 595-596)
      • C99 standard (ISO/IEC 9899:1999):
      • 7.19.6.1 The fprintf function (p: 274-282)
      • 7.19.6.3 The printf function (p: 290)
      • 7.19.6.5 The snprintf function (p: 290-291)
      • 7.19.6.6 The sprintf function (p: 291)
      • C89/C90 standard (ISO/IEC 9899:1990):
      • 4.9.6.1 The fprintf function
      • 4.9.6.3 The printf function
      • 4.9.6.5 The sprintf function

      [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++ documentation forprintf,fprintf,sprintf,snprintf
      Retrieved from "https://en.cppreference.com/mwiki/index.php?title=c/io/fprintf&oldid=179645"
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