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c语言-assert(断言)的笔记

news 来源：原创 2024/5/9 16:10:23

一、assert(断言)简介

assert的功能，条件为真，程序继续执行；如果断言为假（false），则程序终止。

assert是个宏定义！

头文件：

#include <assert.h>

原型：

void assert(scalar expression);

返回值：无返回值。

头文件assert.h内容如下：

/* Copyright (C) 1991-2018 Free Software Foundation, Inc.This file is part of the GNU C Library.The GNU C Library is free software; you can redistribute it and/ormodify it under the terms of the GNU Lesser General PublicLicense as published by the Free Software Foundation; eitherversion 2.1 of the License, or (at your option) any later version.The GNU C Library is distributed in the hope that it will be useful,but WITHOUT ANY WARRANTY; without even the implied warranty ofMERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNULesser General Public License for more details.You should have received a copy of the GNU Lesser General PublicLicense along with the GNU C Library; if not, see<http://www.gnu.org/licenses/>.  *//**  ISO C99 Standard: 7.2 Diagnostics  <assert.h>*/#ifdef  _ASSERT_H# undef  _ASSERT_H
# undef  assert
# undef __ASSERT_VOID_CAST# ifdef  __USE_GNU
#  undef assert_perror
# endif#endif /* assert.h  */#define  _ASSERT_H  1
#include <features.h>#if defined __cplusplus && __GNUC_PREREQ (2,95)
# define __ASSERT_VOID_CAST static_cast<void>
#else
# define __ASSERT_VOID_CAST (void)
#endif/* void assert (int expression);If NDEBUG is defined, do nothing.If not, and EXPRESSION is zero, print an error message and abort.  */#ifdef  NDEBUG# define assert(expr)    (__ASSERT_VOID_CAST (0))/* void assert_perror (int errnum);If NDEBUG is defined, do nothing.  If not, and ERRNUM is not zero, print anerror message with the error text for ERRNUM and abort.(This is a GNU extension.) */# ifdef  __USE_GNU
#  define assert_perror(errnum)  (__ASSERT_VOID_CAST (0))
# endif#else /* Not NDEBUG.  */#ifndef _ASSERT_H_DECLS
#define _ASSERT_H_DECLS
__BEGIN_DECLS/* This prints an "Assertion failed" message and aborts.  */
extern void __assert_fail (const char *__assertion, const char *__file,unsigned int __line, const char *__function)__THROW __attribute__ ((__noreturn__));/* Likewise, but prints the error text for ERRNUM.  */
extern void __assert_perror_fail (int __errnum, const char *__file,unsigned int __line, const char *__function)__THROW __attribute__ ((__noreturn__));/* The following is not at all used here but needed for standardcompliance.  */
extern void __assert (const char *__assertion, const char *__file, int __line)__THROW __attribute__ ((__noreturn__));__END_DECLS
#endif /* Not _ASSERT_H_DECLS *//* When possible, define assert so that it does not add extraparentheses around EXPR.  Otherwise, those added parentheses wouldsuppress warnings we'd expect to be detected by gcc's -Wparentheses.  */
# if defined __cplusplus
#  define assert(expr)              \(static_cast <bool> (expr)            \? void (0)              \: __assert_fail (#expr, __FILE__, __LINE__, __ASSERT_FUNCTION))
# elif !defined __GNUC__ || defined __STRICT_ANSI__
#  define assert(expr)              \((expr)                \? __ASSERT_VOID_CAST (0)            \: __assert_fail (#expr, __FILE__, __LINE__, __ASSERT_FUNCTION))
# else
/* The first occurrence of EXPR is not evaluated due to the sizeof,but will trigger any pedantic warnings masked by the __extension__for the second occurrence.  The ternary operator is required tosupport function pointers and bit fields in this context, and tosuppress the evaluation of variable length arrays.  */
#  define assert(expr)              \((void) sizeof ((expr) ? 1 : 0), __extension__ ({      \if (expr)                \; /* empty */              \else                \__assert_fail (#expr, __FILE__, __LINE__, __ASSERT_FUNCTION);  \}))
# endif# ifdef  __USE_GNU
#  define assert_perror(errnum)            \(!(errnum)                \? __ASSERT_VOID_CAST (0)            \: __assert_perror_fail ((errnum), __FILE__, __LINE__, __ASSERT_FUNCTION))
# endif/* Version 2.4 and later of GCC define a magical variable `__PRETTY_FUNCTION__'which contains the name of the function currently being defined.This is broken in G++ before version 2.6.C9x has a similar variable called __func__, but prefer the GCC one sinceit demangles C++ function names.  */
# if defined __cplusplus ? __GNUC_PREREQ (2, 6) : __GNUC_PREREQ (2, 4)
#   define __ASSERT_FUNCTION  __extension__ __PRETTY_FUNCTION__
# else
#  if defined __STDC_VERSION__ && __STDC_VERSION__ >= 199901L
#   define __ASSERT_FUNCTION  __func__
#  else
#   define __ASSERT_FUNCTION  ((const char *) 0)
#  endif
# endif#endif /* NDEBUG.  */#if defined __USE_ISOC11 && !defined __cplusplus
# undef static_assert
# define static_assert _Static_assert
#endif

assert的定义如下：

此句意思如下：

expr为真，
执行 __ASSERT_VOID_CAST (0)  ;
否则执行 __assert_fail (#expr, __FILE__, __LINE__, __ASSERT_FUNCTION))

条件表达式，伪代码：

a?b:c
//如果a为真，执行b；
//如果a为假，执行c

二、测试代码

参数数量为2，则输出参数。否则输出错误信息，并终止程序执行。测试代码如下：

#include <stdio.h>
#include <assert.h>int main(int argv,char *argc[])
{printf("argv=%d\n",argv);assert(argv== 2);printf("argc[1]=%s\n",argc[1]);return 0;
}