C语言assert(断言)简介
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 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/or modify it under the terms of the gnu lesser general public license as published by the free software foundation; either version 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 of merchantability or fitness for a particular purpose. see the gnu lesser general public license for more details. you should have received a copy of the gnu lesser general public license along with the gnu c library; if not, see . *//* * iso c99 standard: 7.2 diagnostics */#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 #if defined __cplusplus && __gnuc_prereq (2,95)# define __assert_void_cast static_cast#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 an error 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 standard compliance. */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 extra parentheses around expr. otherwise, those added parentheses would suppress warnings we'd expect to be detected by gcc's -wparentheses. */# if defined __cplusplus# define assert(expr) (static_cast ? 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 to support function pointers and bit fields in this context, and to suppress 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 since it 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#endifassert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 #include int main(int argv,char *argc[]){ printf(argv=%dn,argv); assert(argv== 2); printf(argc[1]=%sn,argc[1]); return 0;}
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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 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/or modify it under the terms of the gnu lesser general public license as published by the free software foundation; either version 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 of merchantability or fitness for a particular purpose. see the gnu lesser general public license for more details. you should have received a copy of the gnu lesser general public license along with the gnu c library; if not, see . *//* * iso c99 standard: 7.2 diagnostics */#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 #if defined __cplusplus && __gnuc_prereq (2,95)# define __assert_void_cast static_cast#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 an error 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 standard compliance. */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 extra parentheses around expr. otherwise, those added parentheses would suppress warnings we'd expect to be detected by gcc's -wparentheses. */# if defined __cplusplus# define assert(expr) (static_cast ? 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 to support function pointers and bit fields in this context, and to suppress 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 since it 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#endifassert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 #include int main(int argv,char *argc[]){ printf(argv=%dn,argv); assert(argv== 2); printf(argc[1]=%sn,argc[1]); return 0;}
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