Question

我编写了一个函数，我希望将指针传递给结构数组。我在其中new()，我想用从PGresult结构（res）检索的数据填充它。但是我遇到了错误：

column number 0 is out of range 0..-1 
column number 1 is out of range 0..-1 
column number 2 is out of range 0..-1 
column number 3 is out of range 0..-1
Segmentation fault (core dumped)

这是我的功能

Database::selectAnnouncements(const int user_id, const char *cat_id, struct announcementStruct **pStruct, int *size) {

*size = PQntuples(res);

struct announcementStruct * ann = new struct announcementStruct[PQntuples(res)];
*pStruct =  ann;
int cr_fnum = PQfnumber(res, "created_on");
int con_fnum = PQfnumber(res, "content");
int cat_fnum = PQfnumber(res, "category");
int rm_fnum = PQfnumber(res, "remove_on");


for (int i = 0; i < PQntuples(res); i++) {
        const char *cr_val = PQgetvalue(res, i, cr_fnum);
        const char *con_val = PQgetvalue(res, i, con_fnum);
        const char *cat_val = PQgetvalue(res, i, cat_fnum);
        const char *rm_val = PQgetvalue(res, i, rm_fnum);
        (*pStruct[i]).creation_date = new char[strlen(cr_val)];
        (*pStruct[i]).content = new char[strlen(con_val)];
        (*pStruct[i]).category = new char[strlen(cat_val)];
        (*pStruct[i]).removal_date = new char[strlen(rm_val)];
        strcpy((*pStruct[i]).creation_date, cr_val);
        strcpy((*pStruct[i]).content, con_val);
        strcpy((*pStruct[i]).category, cat_val);
        strcpy((*pStruct[i]).removal_date, rm_val);
}

for (int i = 0; i < PQntuples(res); i++) {
        printf("%s  ", (pStruct[i]->creation_date));
        printf("  %s  ", (pStruct[i]->content));
        printf("  %s  ", (pStruct[i]->category));
        printf("  %s  ", (pStruct[i]->removal_date));
        printf("\n");
}
PQclear(res);

}

这是我如何使用它

struct announcementStruct *announcements = NULL;
int size;
db.selectAnnouncements(0, "DOGS", &announcements, &size);

Answer 1

你肯定忘记了null终止字符串。分配strlen + 1以适合null。忘记null是容易导致段错误的原因。像strncpy snprintf这样的函数有助于确保事情更安全。

凯文的评论也是正确的。确保你得到了这个错误的所有12个实例（原来的4个，strcpy中的4个和printf中的4个）

列号1超出范围0 ..- 1

1 个答案: