按值传递结构

int main（无效） { struct stype baz; baz.foo = malloc（sizeof * baz.foo）; 免费（baz.foo）; bar（baz）; / * UB与否？ * / 返回0; } - Christopher Benson-Manica |我*应该*知道我在说什么 - 如果我 ataru（at）cyberspace.org |不，我需要知道。火焰欢迎。Does the following program exhibit undefined behavior? Specifically,does passing a struct by value cause undefined behavior if that structhas as a member a pointer that has been passed to free()?#include <stdlib.h>struct stype{int *foo;};void bar( struct stype foo ){}int main( void ){struct stype baz;baz.foo=malloc( sizeof *baz.foo );free( baz.foo );bar( baz ); /* UB or not? */return 0;}--Christopher Benson-Manica | I *should* know what I''m talking about - if Iataru(at)cyberspace.org | don''t, I need to know. Flames welcome.推荐答案 2005年12月5日星期一05:20:20 +0000（UTC），Christopher Benson-Manica < at *** @ nospam.cyberspace.org>在comp.lang.c中写道：On Mon, 5 Dec 2005 05:20:20 +0000 (UTC), Christopher Benson-Manica<at***@nospam.cyberspace.org> wrote in comp.lang.c: 以下程序是否表现出未定义的行为？具体来说，按值传递一个struct会导致未定义的行为，如果该结构作为一个成员已经传递给free（）的指针？ 我不知道你为什么要区分由值传递的结构中的指针和通过值传递的裸指针。另外 我不知道为什么你要区分具有 不确定值的指针，因为它未初始化，或者因为它指向 以前分配的存储已被释放。 #include< stdlib.h> struct stype { int * foo ; }; void bar（struct stype foo） {} int main（void） { struct stype baz; baz.foo = malloc（sizeof * baz.foo）; 免费（baz.foo）; bar（baz）; / * UB与否？ * / 返回0; } Does the following program exhibit undefined behavior? Specifically, does passing a struct by value cause undefined behavior if that struct has as a member a pointer that has been passed to free()?I''m not sure why you make a distinction between a pointer in astructure passed by value, and a bare pointer passed by value. AlsoI''m not sure why you make a distinction between a pointer that has anindeterminate value because it is uninitialized, or because it pointsto previously allocated storage that has been freed. #include <stdlib.h> struct stype { int *foo; }; void bar( struct stype foo ) { } int main( void ) { struct stype baz; baz.foo=malloc( sizeof *baz.foo ); free( baz.foo ); bar( baz ); /* UB or not? */ return 0; } 在几个地方，C标准引用函数调用参数 通过赋值存储到函数的参数中。所以将任何东西传递给C中的函数基本上与将函数分配给函数的本地参数值相同。 C中的赋值总是基于值，所以将任何带有 的值除了unsigned char之外的不确定值传递给函数是 未定义的行为，因为任何其他使用这种 对象的价值。具有不确定值的对象是否是结构的一部分没有区别， 值如何变得不确定也没有任何区别。 - Jack Klein 主页： http://JK-Technology.Com 常见问题解答 comp.lang.c http://www.eskimo.com/~scs/C-faq/top.html comp.lang.c ++ http：/ /www.parashift.com/c++-faq-lite/ alt.comp.lang.learn.c-c ++ http：//www.contrib.andrew.cmu.edu/~a ... FAQ-acllc.htmlIn several places, the C standard refers to function call argumentsbeing stored into the function''s parameters by assignment. So passinganything to a function in C is essentially the same as assigning it tothe function''s local parameter value.Assignment in C is always based on value, so passing anything withindeterminate value, other than an unsigned char, to a function isundefined behavior, as is any other use of the value of such anobject. It makes no difference whether the object with indeterminatevalue is part of a structure, nor does it make any difference how thevalue became indeterminate.--Jack KleinHome: http://JK-Technology.ComFAQs forcomp.lang.c http://www.eskimo.com/~scs/C-faq/top.htmlcomp.lang.c++ http://www.parashift.com/c++-faq-lite/alt.comp.lang.learn.c-c++ http://www.contrib.andrew.cmu.edu/~a...FAQ-acllc.html Jack Klein< ja ******* @ spamcop.net>写道：Jack Klein <ja*******@spamcop.net> writes: 2005年12月5日星期一05:20:20 +0000（UTC），Christopher Benson-Manica < at *** @ nospam.cyberspace.org>在comp.lang.c中写道： On Mon, 5 Dec 2005 05:20:20 +0000 (UTC), Christopher Benson-Manica <at***@nospam.cyberspace.org> wrote in comp.lang.c:以下程序是否显示未定义的行为？具体来说，按值传递一个struct导致未定义的行为，如果该结构作为一个成员已经传递给free（）的指针？ Does the following program exhibit undefined behavior? Specifically, does passing a struct by value cause undefined behavior if that struct has as a member a pointer that has been passed to free()? 我''我不确定为什么要区分由值传递的结构中的指针和通过值传递的裸指针。另外我不确定为什么要区分具有不确定值的指针，因为它未初始化，或者因为它指向已释放的先前分配的存储。 I''m not sure why you make a distinction between a pointer in a structure passed by value, and a bare pointer passed by value. Also I''m not sure why you make a distinction between a pointer that has an indeterminate value because it is uninitialized, or because it points to previously allocated storage that has been freed. #include< stdlib.h> struct stype { int * foo; }; void bar（struct stype foo） {} int main（void） { struct stype baz; baz.foo = malloc（sizeof * baz.foo）; 免费（baz.foo）; bar（baz）; / * UB与否？ * / 返回0; } #include <stdlib.h> struct stype { int *foo; }; void bar( struct stype foo ) { } int main( void ) { struct stype baz; baz.foo=malloc( sizeof *baz.foo ); free( baz.foo ); bar( baz ); /* UB or not? */ return 0; } 在几个地方，C标准引用函数调用参数存储到函数中分配参数。因此将任何内容传递给C中的函数与将函数分配给函数的本地参数值基本相同。 C中的赋值始终基于值，因此，除了unsigned char之外，将任何带有不确定值的任何东西传递给函数是未定义的行为，就像使用这样一个对象的值一样。具有不确定值的对象是否是结构的一部分没有区别，值如何变得不确定也没有任何区别。 In several places, the C standard refers to function call arguments being stored into the function''s parameters by assignment. So passing anything to a function in C is essentially the same as assigning it to the function''s local parameter value. Assignment in C is always based on value, so passing anything with indeterminate value, other than an unsigned char, to a function is undefined behavior, as is any other use of the value of such an object. It makes no difference whether the object with indeterminate value is part of a structure, nor does it make any difference how the value became indeterminate. 但DR＃222< http://www.open-std.org/jtc1/sc22/wg14/www/docs/dr_222.htm> 说： 结构或联合对象的值永远不是陷阱 表示，即使结构成员的值或 联合对象可能是一个陷阱代表。 这是在TC2和N1124中发布的。 - Keith Thompson （The_Other_Keith） ks***@mib.org < http://www.ghoti.net/~kst> 圣地亚哥超级计算机中心< *> < http://users.sdsc.edu/~kst> 我们必须做点什么。这是事情。因此，我们必须这样做。But DR #222 <http://www.open-std.org/jtc1/sc22/wg14/www/docs/dr_222.htm>says:The value of a struct or union object is never a traprepresentation, even though the value of a member of a struct orunion object may be a trap representation.This was published in TC2 and in N1124.--Keith Thompson (The_Other_Keith) ks***@mib.org <http://www.ghoti.net/~kst>San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>We must do something. This is something. Therefore, we must do this. Keith Thompson写道：Keith Thompson wrote: Jack Klein< ja ******* @ spamcop.net>写道： Jack Klein <ja*******@spamcop.net> writes: C中的赋值总是基于值，所以传递任何带有不确定值的东西，而不是unsigned char，一个函数是未定义的行为，就像任何其他使用这样一个对象的值一样。具有不确定值的对象是否是一部分没有区别一个结构，也没有任何区别值如何变得不确定。 Assignment in C is always based on value, so passing anything with indeterminate value, other than an unsigned char, to a function is undefined behavior, as is any other use of the value of such an object. It makes no difference whether the object with indeterminate value is part of a structure, nor does it make any difference how the value became indeterminate. 但DR＃222< http://www.open- std.org/jtc1/sc22/wg14/www/docs/dr_222.htm> 说： 结构或联合对象的值永远不是一个陷阱表示，即使结构或联合对象的成员的值可能是陷阱表示。 这是在TC2和N1124中发布的。 But DR #222 <http://www.open-std.org/jtc1/sc22/wg14/www/docs/dr_222.htm> says: The value of a struct or union object is never a trap representation, even though the value of a member of a struct or union object may be a trap representation. This was published in TC2 and in N1124. 我不认为与访问释放的指针值相关的未定义行为 与陷阱有任何关系。 - peteI don''t think that the undefined behaviorassociated with accessing freed pointer valueshas anything to do with traps.--pete 这篇关于按值传递结构的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！ 上岸，阿里云！