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The formatted output functions (fprintf() and related functions) convert, format, and print their arguments under control of a format string. The C Standard, 7.2123.6.1, paragraph 3 [ISO/IEC 9899:20112024], specifies

The format shall be a multibyte character sequence, beginning and ending in its initial shift state. The format is composed of zero or more directives: ordinary multibyte characters (not %), which are copied unchanged to the output stream; and conversion specifications, each of which results in fetching zero or more subsequent arguments, converting them, if applicable, according to the corresponding conversion specifier, and then writing the result to the output stream.

...

Zero or more flags (in any order), which modify the meaning of the conversion specification
An optional minimum field width
An optional precision that gives the minimum number of digits, the maximum number of digits to appear for certain conversion specifiers, or the maximum number of bytes, etc. depending on the conversion specifier
An optional length modifier that specifies the size of the argument
A conversion specifier character that indicates the type of conversion to be applied

...

Valid and meaningful combinations are marked by the symbol (save for the length modifier columns, as described previously). Valid combinations that have no effect are labeled N/E. Using a combination marked by the symbol, using a specification not represented in the table, or using an argument of an unexpected type is undefined behavior. (See undefined behaviors 153 158, 155 160, 157 162, 158 163, 161 166, and 162 167.)

Conversion Specifier Character	`h`	`hh`	`l`	`ll`	`j`	`z`	`t`	`L`	Argument Type
`d`, `i`	`short`	`signed char`	`long`	`long long`	`intmax_t`	`size_t`	`ptrdiff_t`		Signed integer
`o`	`unsigned` `short`	`unsigned char`	`unsigned long`	`unsigned long long`	`uintmax_t`	`size_t`	`ptrdiff_t`		Unsigned integer
`u`	`unsigned short`	`unsigned char`	`unsigned long`	`unsigned long long`	`uintmax_t`	`size_t`	`ptrdiff_t`		Unsigned integer
`x`, `X`	`unsigned short`	`unsigned char`	`unsigned long`	`unsigned long long`	`uintmax_t`	`size_t`	`ptrdiff_t`		Unsigned integer
`f`, `F`			N/E	N/E				`long double`	`double` or `long double`
`e`, `E`			N/E	N/E				`long double`	`double` or `long double`
`g`, `G`			N/E	N/E				`long double`	`double` or `long double`
`a`, `A`			N/E	N/E				`long double`	`double` or `long double`
`c`			`wint_t`						`int` or `wint_t`
`s`			NTWS						NTBS or NTWS
`p`									`void*`
`n`	`short*`	`char*`	`long*`	`long long*`	`intmax_t*`	`size_t*`	`ptrdiff_t*`		Pointer to integer
`C` ^XSI									`wint_t`
`S` ^XSI									NTWS
`%`									None

     SPACE: The space (" ") character
     N/E: No effect
     NTBS: char* argument pointing to a null-terminated character string
     NTWS: wchar_t* argument pointing to a null-terminated wide character string
     XSI: ISO/IEC 9945-2003 XSI extension

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Mismatches between arguments and conversion specifications may result in undefined behavior 163. Compilers may diagnose type mismatches in formatted output function invocations. In this noncompliant code example, the error_type argument to printf() is incorrectly matched with the s specifier rather than with the d specifier. Likewise, the error_msg argument is incorrectly matched with the d specifier instead of the s specifier specifier. These usages result in undefined behavior 163. One possible result of this invocation is that printf() will interpret the error_type argument as a pointer and try to read a string from the address that error_type contains, possibly resulting in an access violation.

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Incorrectly specified format strings can result in memory corruption or abnormal program termination.

Rule	Severity	Likelihood	Detectable	Remediation CostRepairable	Priority	Level
FIO47-C	High	Unlikely	Yes	NoMedium	P6	L2

Automated Detection

0161, 0162, 0163, 0164, 0165, 0166, 0167, 0168, 0169,

0170, 0171, 0172, 0173, 0174, 0175, 0176, 0177, 0178,

0179 [U], 0180 [C99], 0184 [U], 0185 [U], 0190 [U],

0191 [U], 0192 [U], 0193 [U], 0194 [U], 0195 [U], 0196 [U],

0197 [U], 0198 [U], 0199 [U], 0200 [U], 0201 [U], 0202 [I],

0204 [U], 0206 [U]

Tool

Version

Checker

Description

Axivion Bauhaus Suite

Include Page

	Axivion Bauhaus Suite_V
	Axivion Bauhaus Suite_V

CertC-FIO47

Fully implemented

CodeSonar

Include Page

	CodeSonar_V
	CodeSonar_V

IO.INJ.FMT
MISC.FMT
MISC.FMTTYPE

Format string injection
Format string
Format string type error

Coverity

Include Page

	Coverity_V
	Coverity_V

PW

Reports when the number of arguments differs from the number of required arguments according to the format string

Cppcheck

Include Page

	Cppcheck_V
	Cppcheck_V

invalidscanf
wrongPrintfScanfArgNum
invalidLengthModifierError
invalidScanfFormatWidth
wrongPrintfScanfParameterPositionError

Cppcheck Premium

Include Page

	Cppcheck Premium_V
	Cppcheck Premium_V

invalidscanf
wrongPrintfScanfArgNum
invalidLengthModifierError
invalidScanfFormatWidth
wrongPrintfScanfParameterPositionError

GCC

Include Page

	GCC_V
	GCC_V

Can detect violations of this recommendation when the -Wformat flag is used

Helix QAC

Include Page

	Helix QAC_V
	Helix QAC_V

C0161, C0162, C0163, C0164, C0165, C0166, C0167, C0168, C0169, C0170, C0171, C0172, C0173, C0174, C0175, C0176, C0177, C0178, C0179, C0180, C0184, C0185, C0190, C0191, C0192, C0193, C0194, C0195, C0196, C0197, C0198, C0199, C0200, C0201, C0202, C0204, C0206, C0209

C++3150, C++3151, C++3152, C++3153, C++3154, C++3155, C++3156, C++3157, C++3158, C++3159

Klocwork

Include Page

	Klocwork_V
	Klocwork_V

SV.FMT_STR.PRINT_FORMAT_MISMATCH.BAD
SV.FMT_STR.PRINT_FORMAT_MISMATCH.UNDESIRED
SV.FMT_STR.PRINT_IMPROP_LENGTH
SV.FMT_STR.PRINT_PARAMS_WRONGNUM.FEW
SV.FMT_STR.PRINT_PARAMS_WRONGNUM.MANY
SV.FMT_STR.SCAN_FORMAT_MISMATCH.BAD
SV.FMT_STR.SCAN_FORMAT_MISMATCH.UNDESIRED
SV.FMT_STR.SCAN_IMPROP_LENGTH
SV.FMT_STR.SCAN_PARAMS_WRONGNUM.FEW
SV.FMT_STR.SCAN_PARAMS_WRONGNUM.MANY
SV.FMT_STR.UNKWN_FORMAT

LDRA tool suite

Include Page

	LDRA_V
	LDRA_V

486 S
589 S

Fully implemented

Parasoft C/C++test

Include Page

	Parasoft_V
	Parasoft_V

CERT_C-FIO47-a
CERT_C-FIO47-b
CERT_C-FIO47-c
CERT_C-FIO47-d
CERT_C-FIO47-e
CERT_C-FIO47-f

There should be no mismatch between the '%s' and '%c' format specifiers in the format string and their corresponding arguments in the invocation of a string formatting function
There should be no mismatch between the '%f' format specifier in the format string and its corresponding argument in the invocation of a string formatting function
There should be no mismatch between the '%i' and '%d' format specifiers in the string and their corresponding arguments in the invocation of a string formatting function
There should be no mismatch between the '%u' format specifier in the format string and its corresponding argument in the invocation of a string formatting function
There should be no mismatch between the '%p' format specifier in the format string and its corresponding argument in the invocation of a string formatting function
The number of format specifiers in the format string and the number of corresponding arguments in the invocation of a string formatting function should be equal

PC-lint Plus

Include Page