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Preface Overview of the Compiler Getting Started with the Compiler Compiler Features Compiler Coding Practices Compiler Diagnostic Messages Using the Inline and Embedded Assemblers of the AR Compiler Command-line Options Language Extensions Compiler-specific Features Keywords and operators __align __ALIGNOF__ __alignof__ __asm __forceinline __global_reg __inline __int64 __INTADDR__ __irq __packed __pure __smc __softfp __svc __svc_indirect __svc_indirect_r7 __value_in_regs __weak __writeonly __declspec attributes __declspec(noinline) __declspec(noreturn) __declspec(nothrow) __declspec(notshared) __declspec(thread) Function attributes __attribute__((alias)) function attribute __attribute__((always_inline)) function attribute __attribute__((const)) function attribute __attribute__((deprecated)) function attribute __attribute__((destructor[(priority)])) function a __attribute__((format)) function attribute __attribute__((format_arg(string-index))) function __attribute__((malloc)) function attribute __attribute__((noinline)) function attribute __attribute__((no_instrument_function)) function a __attribute__((nomerge)) function attribute __attribute__((nonnull)) function attribute __attribute__((noreturn)) function attribute __attribute__((notailcall)) function attribute __attribute__((nothrow)) function attribute __attribute__((pcs("calling_convention"))) functio __attribute__((pure)) function attribute __attribute__((section("name"))) function attribut __attribute__((sentinel)) function attribute __attribute__((unused)) function attribute __attribute__((used)) function attribute __attribute__((visibility("visibility_type"))) fun __attribute__((warn_unused_result)) __attribute__((weak)) function attribute __attribute__((weakref("target"))) function attrib Type attributes __attribute__((bitband)) type attribute __attribute__((aligned)) type attribute __attribute__((packed)) type attribute Variable attributes __attribute__((alias)) variable attribute __attribute__((at(address))) variable attribute __attribute__((aligned)) variable attribute __attribute__((deprecated)) variable attribute __attribute__((noinline)) constant variable attrib __attribute__((packed)) variable attribute __attribute__((section("name"))) variable attribut __attribute__((unused)) variable attribute __attribute__((used)) variable attribute __attribute__((visibility("visibility_type"))) var __attribute__((weak)) variable attribute __attribute__((weakref("target"))) variable attrib __attribute__((zero_init)) variable attribute Pragmas #pragma anon_unions, #pragma no_anon_unions #pragma arm #pragma arm section [section_type_list] #pragma diag_default tag[,tag,...] #pragma diag_error tag[,tag,...] #pragma diag_remark tag[,tag,...] #pragma diag_suppress tag[,tag,...] #pragma diag_warning tag[, tag, ...] #pragma exceptions_unwind, #pragma no_exceptions_u #pragma GCC system_header #pragma hdrstop #pragma import symbol_name #pragma import(__use_full_stdio) #pragma import(__use_smaller_memcpy) #pragma inline, #pragma no_inline #pragma no_pch #pragma Onum #pragma once #pragma Ospace #pragma Otime #pragma pack(n) #pragma pop #pragma push #pragma softfp_linkage, #pragma no_softfp_linkage #pragma thumb #pragma unroll [(n)] #pragma unroll_completely #pragma weak symbol, #pragma weak symbol1 = symbol Instruction intrinsics __breakpoint intrinsic __cdp intrinsic __clrex intrinsic __clz intrinsic __current_pc intrinsic __current_sp intrinsic __disable_fiq intrinsic __disable_irq intrinsic __dmb intrinsic __dsb intrinsic __enable_fiq intrinsic __enable_irq intrinsic __fabs intrinsic __fabsf intrinsic __force_loads intrinsic __force_stores intrinsic __isb intrinsic __ldrex intrinsic __ldrexd intrinsic __ldrt intrinsic __memory_changed intrinsic __nop intrinsic __pld intrinsic __pli intrinsic __qadd intrinsic __qdbl intrinsic __qsub intrinsic __rbit intrinsic __rev intrinsic __return_address intrinsic __ror intrinsic __schedule_barrier intrinsic __semihost intrinsic __sev intrinsic __sqrt intrinsic __sqrtf intrinsic __ssat intrinsic __strex intrinsic __strexd intrinsic __strt intrinsic __swp intrinsic __usat intrinsic __wfe intrinsic __wfi intrinsic __yield intrinsic ARMv6 SIMD intrinsics ETSI basic operations C55x intrinsics VFP status intrinsic __vfp_status intrinsic Fused Multiply Add (FMA) intrinsics Named register variables GNU built-in functions Predefined macros Built-in function name variables C and C++ Implementation Details What is Semihosting? Via File Syntax Summary Table of GNU Language Extensions Standard C Implementation Definition Standard C++ Implementation Definition C and C++ Compiler Implementation Limits
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__attribute__((format)) function attribute

Non-ConfidentialPDF file icon PDF versionARM DUI0375H
ARM® Compiler v5.06 for µVision® armcc User GuideVersion 5
Home > Compiler-specific Features > __attribute__((format)) function attribute

9.34 __attribute__((format)) function attribute

This attribute causes the compiler to check that the supplied arguments are in the correct format for the specified function.

Syntax

__attribute__((format(function, string-index, first-to-check)))
Where function is a printf-style function, such as printf(), scanf(), strftime(), gnu_printf(), gnu_scanf(), gnu_strftime(), or strfmon().
string-index specifies the index of the string argument in your function (starting from one).
first-to-check is the index of the first argument to check against the format string.

Example

#include <stdio.h>

extern char *myFormatText1 (const char *, ...);
extern char *myFormatText2 (const char *, ...) __attribute__((format(printf, 1, 2)));


int main(void) {
  int a, b;
  float c;

  a = 5;
  b = 6;
  c = 9.099999;

myFormatText1("Here are some integers: %d , %d\n", a, b); // No type checking. Types match.
myFormatText1("Here are some integers: %d , %d\n", a, c); // No type checking. Type mismatch, but no warning.


myFormatText2("Here are some integers: %d , %d\n", a, b); // Type checking. Types match.
myFormatText2("Here are some integers: %d , %d\n", a, c); // Type checking. Warning: 181-D: argument is incompatible...
}
myFormatText1() is a function that is given a string and two arguments to print. It has no format checking, so when it is passed a float argument and the function is expecting an integer, there is a silent type-mismatch.
myFormatText2() is identical to myFormatText1(), except it has __attribute__((format())). When it receives an argument of an unexpected type, it raises a warning message.
Related reference
Non-ConfidentialPDF file icon PDF versionARM DUI0375H
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