bsearch脚本段错误 [英] bsearch script segfault
问题描述
我有一个非常简单的脚本，它使用bsearch来查找
特定元素
问题是，它只是在比较中的段错误功能。
我有一个类似的脚本工作正常，现在这只是段错误。
我开车自己疯了，最后4小时，为什么这样一个简单的事情会
不工作
请有人帮忙
谢谢
Ram
#include< stdlib.h>
#include< stdio.h>
#include< string.h>
struct aliasid {
char a_id [100];
int count;
};
int compare_aliases（const void * p1，const void * p2）{
const struct aliasid * u1 =（const struct aliasid *）p1;
const struct aliasid ** u2 =（const struct aliasid **）p2;
return（strcmp（u1-> a_id，（* u2） - > a_id））;
}
struct aliasid * new_aliasid（char * id，int numids）{
struct aliasid * a;
a = malloc（sizeof（struct aliasid）+10）;
strcpy（a-> a_id，id ）;
a-> count = 0;
返回（a）;
}
int main（int argc，char * argv []）{
struct aliasid ** aliases，** tmp1;
char the_string [100];
别名= malloc（3 * sizeof（void *））;
if（别名== NULL）{
printf（" malloc失败"）;
退出（1）;
}
别名[0] = new_aliasid（" abc"，3）;
别名[1] = new_aliasid（" def"，3）;
别名[2] = NULL;
tmp1 =（struct aliasid **）bsearch（" abc"，aliases，2，sizeof（struct
aliasid），compare_aliases）;
if（tmp1 == NULL ）{
printf（" id％s was found\\\
，the_string）;
} else {
printf（ id％s被发现了\ n，the_string）;
}
返回（0）;
}
I have got a pretty simple script , that uses bsearch to look for a
particular element
The problem is , it simply segfaults inside the compare function.
I have a similar script that works fine , and now this simply segfaults.
I am driving myself nuts , last 4 hrs , why such a simple thing would
not work
Pls someone help
Thanks
Ram
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
struct aliasid {
char a_id[100];
int count;
};
int compare_aliases(const void *p1, const void *p2 ){
const struct aliasid *u1 = (const struct aliasid *) p1;
const struct aliasid **u2 = (const struct aliasid **) p2;
return(strcmp(u1->a_id,(*u2)->a_id));
}
struct aliasid* new_aliasid(char* id,int numids) {
struct aliasid* a;
a = malloc(sizeof(struct aliasid) +10);
strcpy(a->a_id,id);
a->count = 0;
return(a);
}
int main(int argc,char* argv[]){
struct aliasid **aliases , **tmp1;
char the_string[100];
aliases = malloc(3 * sizeof(void*));
if(aliases == NULL ) {
printf("malloc failed");
exit(1);
}
aliases[0]= new_aliasid("abc",3);
aliases[1]= new_aliasid("def",3);
aliases[2]=NULL;
tmp1 = (struct aliasid **) bsearch("abc",aliases,2,sizeof( struct
aliasid),compare_aliases);
if(tmp1 == NULL){
printf("The id %s was not found\n",the_string);
} else {
printf("The id %s was found\n",the_string);
}
return(0);
}
推荐答案
Ramprasad A Padmanabhan写道：
Ramprasad A Padmanabhan wrote:
我有一个非常简单的脚本，它使用bsearch来寻找
特殊元素
问题是，它只是在比较函数中的段错误。
我有一个类似的脚本工作正常，现在这只是段错误。我开车自己疯了，最后4小时，为什么这么简单的事情会不起作用
请别人帮忙
谢谢
Ram
#include< stdlib.h>
#include< stdio.h>
#include< string.h>
struct aliasid {
char a_id [100];
int count;
};
int compare_aliases（const void * p1，const void * p2）{
const struct aliasid * u1 =（const struct aliasid *）p1;
const struct aliasid ** u2 =（const struct aliasid **）p2;
return（strcmp（u1-> a_id，（* u2） - > a_id）） ;
}
struct aliasid * a;
a = malloc（sizeof（struct aliasid）+10）;
strcpy（a-> a_id，id）;
a-> count = 0;
返回（a）;
}
int main（int argc，char * argv []）{
struct aliasid **别名，** tmp1;
char the_string [100];
别名= malloc（3 * sizeof（void *））;
if（别名== NULL）{
printf（" malloc failed"）;
exit（1）;
}
别名[0] = new_aliasid（" abc"，3）;
别名[1] = new_aliasid（" def"，3）;
别名[2] = NULL;
tmp1 =（struct aliasid **）bsearch（" abc"，aliases， 2，sizeof（struct
aliasid），compare_aliases）;
if（tmp1 == NULL）{
printf（" id％s was found\\\
" ，the_string）;
} else {
printf（" id％s was found\\\
，the_string）;
}
return（0） ;
}
I have got a pretty simple script , that uses bsearch to look for a
particular element
The problem is , it simply segfaults inside the compare function.
I have a similar script that works fine , and now this simply segfaults.
I am driving myself nuts , last 4 hrs , why such a simple thing would
not work
Pls someone help
Thanks
Ram
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
struct aliasid {
char a_id[100];
int count;
};
int compare_aliases(const void *p1, const void *p2 ){
const struct aliasid *u1 = (const struct aliasid *) p1;
const struct aliasid **u2 = (const struct aliasid **) p2;
return(strcmp(u1->a_id,(*u2)->a_id));
}
struct aliasid* new_aliasid(char* id,int numids) {
struct aliasid* a;
a = malloc(sizeof(struct aliasid) +10);
strcpy(a->a_id,id);
a->count = 0;
return(a);
}
int main(int argc,char* argv[]){
struct aliasid **aliases , **tmp1;
char the_string[100];
aliases = malloc(3 * sizeof(void*));
if(aliases == NULL ) {
printf("malloc failed");
exit(1);
}
aliases[0]= new_aliasid("abc",3);
aliases[1]= new_aliasid("def",3);
aliases[2]=NULL;
tmp1 = (struct aliasid **) bsearch("abc",aliases,2,sizeof( struct
aliasid),compare_aliases);
if(tmp1 == NULL){
printf("The id %s was not found\n",the_string);
} else {
printf("The id %s was found\n",the_string);
}
return(0);
}
好吧，我想我遇到了问题，
如果我将别名声明为
*别名[3];
那么这个工作正常
这是否意味着我无法动态地为结构分配内存
数组我在bsearch中使用
谢谢
Ram
Ok , I think I have got the problem ,
If I declare aliases as
*aliases[3];
Then this works fine
So does that mean I cannot dynamically allocate memory to a structure
array Which I use in bsearch
Thanks
Ram
Ramprasad A Padmanabhan< ra ******* @ netcore.co.in>写道：
Ramprasad A Padmanabhan <ra*******@netcore.co.in> wrote:
我有一个非常简单的脚本，它使用bsearch来寻找特定元素
问题是，它只是在比较函数中的段错误。
我有一个类似的脚本，工作正常，现在这只是段错误。
我开车自己疯了，最后4小时，为什么这么简单的事情将无法工作
＃ include< stdlib.h>
#include< stdio.h>
#include< string.h>
struct aliasid {
char a_id [100];
int count;
};
int compare_aliases（const void * p1，const void * p2）{
const struct aliasid * u1 =（const struct aliasid *）p1;
const struct aliasid ** u2 =（const struct aliasid **）p2;
为什么p2是指向指针的指针？那不是
很有意义。
return（strcmp（u1-> a_id，（* u2） - > a_id））;
}
struct aliasid * new_aliasid（char * id，int numids）{
struct aliasid * a;
a = malloc（sizeof（struct aliasid）+10）;
为什么要分配比你需要的多10个字节？如果你把它写成
a = malloc（sizeof * a + 10），那么维护（和阅读）的东西将会很轻松。
strcpy（a-> a_id，id）;
a-> count = 0;
return（a）;
}
int main（int argc，char * argv []）{
struct aliasid ** aliases，** tmp1;
char the_string [100];
aliases = malloc（3 * sizeof（void *））;
为什么sizeof（void *）？你显然想要一组结构指针。
只需把它写成
别名= malloc（3 * sizeof *别名）;
if（别名== NULL）{
printf（" malloc failed"）;
exit（1）;
}
别名[0] = new_aliasid（" abc"，3）;
别名[1] = new_aliasid（" def"，3）;
别名[2] = NULL;
tmp1 =（struct aliasid **）bsearch（ abc，别名，2，sizeof（struct
aliasid），compare_aliases）;
这里绝对错误的是''size''参数，即第四个
参数：你传递给bsearch（）的是一个数组*指针*，而不是
。使'sizeof *别名''你应该没事。
你不需要演员，就像malloc（）一样，它只会保持
编译来自抱怨，如果你忘了包含< stdlib.h>
if（tmp1 == NULL）{
printf（" id％s未找到） \ n"，the_string）;
} else {
printf（" id％s was found\\\
，the_string）;
''the_string''从未被赋值，所以你不能打印它。
}
返回（0） ;
难道你不能自己清理并释放你分配的记忆;-)
}
I have got a pretty simple script , that uses bsearch to look for a
particular element The problem is , it simply segfaults inside the compare function. I have a similar script that works fine , and now this simply segfaults.
I am driving myself nuts , last 4 hrs , why such a simple thing would
not work #include <stdlib.h>
#include <stdio.h>
#include <string.h> struct aliasid {
char a_id[100];
int count;
};
int compare_aliases(const void *p1, const void *p2 ){
const struct aliasid *u1 = (const struct aliasid *) p1;
const struct aliasid **u2 = (const struct aliasid **) p2;
Why do you have p2 being a pointer to a pointer? That doesn''t
make much sense.
return(strcmp(u1->a_id,(*u2)->a_id));
} struct aliasid* new_aliasid(char* id,int numids) {
struct aliasid* a;
a = malloc(sizeof(struct aliasid) +10);
Why do you allocate 10 more bytes than you need? And things would be a
lot easer to maintain (and to read) if you would write this as
a = malloc( sizeof *a + 10 );
strcpy(a->a_id,id);
a->count = 0;
return(a);
} int main(int argc,char* argv[]){
struct aliasid **aliases , **tmp1;
char the_string[100]; aliases = malloc(3 * sizeof(void*));
Why sizeof(void*)? You obviously want a array of structure pointers.
Just write it as
aliases = malloc( 3 * sizeof *aliases );
if(aliases == NULL ) {
printf("malloc failed");
exit(1);
}
aliases[0]= new_aliasid("abc",3);
aliases[1]= new_aliasid("def",3);
aliases[2]=NULL;
tmp1 = (struct aliasid **) bsearch("abc",aliases,2,sizeof( struct
aliasid),compare_aliases);
What''s definitely wrong here is the ''size'' argument, i.e. the fourth
argument: what you pass to bsearch() is an array *of pointers*, not
of structures. That''s the most likely reason for the crash you''re
seeing. Make that ''sizeof *aliases'' and you should be fine.
And you don''t need the cast, like for malloc() it will only keep the
compiler from complaining if you forgot to include <stdlib.h>
if(tmp1 == NULL){
printf("The id %s was not found\n",the_string);
} else {
printf("The id %s was found\n",the_string);
''the_string'' never has been assigned a value, so you can''t print it.
}
return(0);
Shouldn''t you clean up after yourself and free the memory you allocated;-)
}
问候，Jens
-
\ Jens Thoms Toerring ___ Je *********** @ physik.fu-berlin.de
\ __________________________ http://www.physik.fu-berlin.de/~toerring
Ramprasad A Padmanabhan< ra ******* @ netcore.co.in>这样说：
Ramprasad A Padmanabhan <ra*******@netcore.co.in> spoke thus:
我有一个非常简单的脚本，它使用bsearch寻找
I have got a pretty simple script , that uses bsearch to look for a
-
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。
<pedantry>A C program isn''t technically a "script," is it?</pedantry>
--
Christopher Benson-Manica | I *should* know what I''m talking about - if I
ataru(at)cyberspace.org | don''t, I need to know. Flames welcome.
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