指向另一个结构的指针，写入并从文件中读取给出SegFault [英] pointer to one struct in another, writing and reading it from file gives SegFault
问题描述
我正在做Extra Credits部分。让数据库代码在该页上给出
我试图改变代码来接受MAX_DATA和MAX_ROWS的参数，将它们存储在数据库中结构，并写入到文件，从而创建一个可以任意大小的数据库
$ $ p $ $ $ $ c $ struct结构地址{
int id;
int set;
char * name;
char * email;
};
struct数据库{
int MAX_DATA;
int MAX_ROWS;
struct地址*行;
};这样，我就可以从用户那里得到MAX_DATA和MAX_ROWS参数来创建一个数据库，就像他自己的数据库一样喜好。我在代码中修改的其他东西是：
$ b $ p Database_create函数：
$ $ $ $ $ $ $ c $ void $ Database_create（struct Connection * conn，int MAX_DATA，int MAX_ROWS）
{
int i = 0;
conn-> db-> MAX_DATA = MAX_DATA;
conn-> db-> MAX_ROWS = MAX_ROWS;
conn-> db-> rows = malloc（sizeof（struct Address）* MAX_ROWS）;
for（i = 0; i< MAX_ROWS; i ++）{
struct Address addr = {.id = i，.set = 0};
conn-> db-> rows [i] = addr;
$ / code $ / pre
字节，SegFault是：
$ b $ pre $ void $ Database_set（struct Connection * conn，int id，const char * name，const char * email）
{
struct Address * addr =& conn-> db-> rows [id];
int MAX_DATA = conn-> db-> MAX_DATA;
if（addr-> set）die（已经设置，先删除）;
/ *这个if语句给addr-> set * /
addr-> set = 1;
addr-> name = malloc（sizeof（char）* MAX_DATA）;
addr-> email = malloc（sizeof（char）* MAX_DATA）;
//警告：错误，阅读如何打破它并修复这个
char * res = strncpy（addr-> name，name，MAX_DATA）;
//演示strncpy bug
if（！res）die（Name copy failed）;
res = strncpy（addr-> email，email，MAX_DATA）;
if（！res）die（Email copy failed）;
}
我知道这个代码片段不是整个部分，在这里粘贴整个代码。
所以，我已经发布在这里： http://pastebin.com/EbKShT3r
我可以使用'c'选项创建和编写首次运行的数据库。但是，要使用's'选项添加条目，会发生分段错误。
编辑：
最后，我得到这个程序使用@WhizCraig给出的解决方案
，为了释放内存，这里是我正在尝试：
$ pre $ void $ Database_close（struct Connection * conn）
{
int i;
if（conn）{
int MAX_ROWS = conn-> db-> MAX_ROWS;
for（i = 0; i< MAX_ROWS; i ++）{
struct address * row = conn-> db-> rows + i;
if（row-> set）{
free（row-> name）;
free（row-> email）;
free（conn-> db-> rows）;
if（conn-> file）fclose（conn-> file）;
if（conn-> db）free（conn-> db）;
free（conn）;
$ b $ p
$ b我的错误Valgrind，是泄漏。我不明白上面的代码中的错误。
然而，主要的问题似乎已经解决了：）
struct地址{
int id;
int set;
char * name;
char * email;
};
struct数据库{
int MAX_DATA;
int MAX_ROWS;
地址**行; //使用指针阵列
};
void Database_create（Connection * conn，int MAX_DATA，int MAX_ROWS）
{
int i = 0;
conn-> db-> MAX_DATA = MAX_DATA;
conn-> db-> MAX_ROWS = MAX_ROWS;
conn-> db-> rows =（Address **）malloc（sizeof（Address *）* MAX_ROWS）; （i = 0; i< MAX_ROWS; i ++）{
conn-> db-> rows [i] =（Address *）malloc（sizeof（Address））
;
conn-> db-> rows [i] - > id = i;
conn-> db-> rows [i] - > set = 0;
$ b void Database_set（Connection * conn，int id，const char * name，const char * email）
{
if（！ （conn& conn-> db& conn-> db-> rows& conn-> db-> rows [id]））return;
地址* addr = conn-> db-> rows [id];
int MAX_DATA = conn-> db-> MAX_DATA;
if（addr-> set == 0）die（已经设置，先删除）;
addr-> set = 1;
addr-> name = malloc（sizeof（char）* MAX_DATA）;
addr-> email = malloc（sizeof（char）* MAX_DATA）;
$ b $ char * res = strncpy（addr-> name，name，MAX_DATA）;
if（！res）die（Name copy failed）;
res = strncpy（addr-> email，email，MAX_DATA）;
if（！res）die（Email copy failed）;
}
void Database_close（Connection * conn）
{
size_t i;如果（conn）{
if（con> db& conn-> db-> rows）{
for（i = 0; i< conn- > db-> MAX_ROWS; i ++）{
Address * cur = conn-> db-> rows [i];
free（cur）;
$ b if（conn-> file）fclose（conn-> file）;
if（conn-> db）free（conn-> db）;
free（conn）;
}
}
I am brushing up my C skills from Learn C The Hard Way, currently I am at 17th Exercise.
I am doing the 'Extra Credits' part. Making the database code given on that page to get I am trying to
"Change the code to accept parameters for MAX_DATA and MAX_ROWS, store them in the Database struct, and write that to the file, thus creating a database that can be arbitrarily sized"
So, I commented out the #define directives, and changed Address and Database structs as given:
struct Address {
int id;
int set;
char *name;
char *email;
};
struct Database {
int MAX_DATA;
int MAX_ROWS;
struct Address *rows;
};
So that, I can get MAX_DATA, and MAX_ROWS parameters from the user to create a database as per his liking. Other things I changed in the code are --
The Database_create function :
void Database_create(struct Connection *conn, int MAX_DATA, int MAX_ROWS)
{
int i = 0;
conn->db->MAX_DATA = MAX_DATA;
conn->db->MAX_ROWS = MAX_ROWS;
conn->db->rows = malloc(sizeof(struct Address) * MAX_ROWS);
for(i = 0; i < MAX_ROWS; i++) {
struct Address addr = {.id = i, .set = 0};
conn->db->rows[i] = addr;
}
}
The part where I am getting 'Invalid read of 4 bytes', and SegFault is :
void Database_set(struct Connection *conn, int id, const char *name, const char *email)
{
struct Address *addr = &conn->db->rows[id];
int MAX_DATA = conn->db->MAX_DATA;
if(addr->set) die("Already set, delete it first");
/* This if statement gives error for addr->set */
addr->set = 1;
addr->name = malloc(sizeof(char) * MAX_DATA);
addr->email = malloc(sizeof(char) * MAX_DATA);
// WARNING: bug, read the "How To Break It" and fix this
char *res = strncpy(addr->name, name, MAX_DATA);
// demonstrate the strncpy bug
if(!res) die("Name copy failed");
res = strncpy(addr->email, email, MAX_DATA);
if(!res) die("Email copy failed");
}
I know this code snippets isn't the whole part, but I can't paste the whole code here. So, I've posted it here : http://pastebin.com/EbKShT3r I can create and write database for the first run using 'c' option. However, to add entries using 's' option, the Segmentation Fault occurs.
EDIT : So, Finally, I got this program working with the solution given under by @WhizCraig However, for freeing the memory, here is what I am trying :
void Database_close(struct Connection *conn)
{
int i;
if (conn) {
int MAX_ROWS = conn->db->MAX_ROWS;
for (i=0; i<MAX_ROWS; i++) {
struct Address *row = conn->db->rows+i;
if (row->set) {
free(row->name);
free(row->email);
}
}
free(conn->db->rows);
if(conn->file) fclose(conn->file);
if(conn->db) free(conn->db);
free(conn);
}
}
And, I am getting errors in Valgrind, memory is leaking. I don't understand the error in above code. However, the main problem appears to be solved :)
struct Address {
int id;
int set;
char *name;
char *email;
};
struct Database {
int MAX_DATA;
int MAX_ROWS;
Address **rows; // USE ARRAY OF POINTERS
};
void Database_create(Connection *conn, int MAX_DATA, int MAX_ROWS)
{
int i = 0;
conn->db->MAX_DATA = MAX_DATA;
conn->db->MAX_ROWS = MAX_ROWS;
conn->db->rows = (Address**)malloc(sizeof(Address*) * MAX_ROWS);
for(i = 0; i < MAX_ROWS; i++) {
conn->db->rows[i] = (Address*)malloc(sizeof(Address));
conn->db->rows[i]->id = i;
conn->db->rows[i]->set = 0;
}
}
void Database_set(Connection *conn, int id, const char *name, const char *email)
{
if (!(conn && conn->db && conn->db->rows && conn->db->rows[id])) return;
Address *addr = conn->db->rows[id];
int MAX_DATA = conn->db->MAX_DATA;
if(addr->set == 0) die("Already set, delete it first");
addr->set = 1;
addr->name = malloc(sizeof(char) * MAX_DATA);
addr->email = malloc(sizeof(char) * MAX_DATA);
char *res = strncpy(addr->name, name, MAX_DATA);
if(!res) die("Name copy failed");
res = strncpy(addr->email, email, MAX_DATA);
if(!res) die("Email copy failed");
}
void Database_close(Connection *conn)
{
size_t i;
if(conn) {
if (con->db && conn->db->rows) {
for (i = 0; i < conn->db->MAX_ROWS; i++) {
Address *cur = conn->db->rows[i];
free(cur);
}
}
if(conn->file) fclose(conn->file);
if(conn->db) free(conn->db);
free(conn);
}
}
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