当mysql_stmt_close时出现段错误
当mysql_stmt_close时出现段错误
提问于 2012-10-01 00:24:40
我正在尝试使用C API查询MySQL5.5。
dbutil.c包含样板代码：
#include "../include/dbutil.h"
#include "../include/logging.h"
#include "../include/common.h"
MYSQL get_connection(char *host, char *user, char *passwd, char *db) {
MYSQL conn;
mysql_init(&conn);
if (!mysql_real_connect(&conn, host, user, passwd, db, 0, NULL, 0)) {
log_to_console("Cannot connect to MySQL server: %s", mysql_error(&conn));
exit(1);
}
return conn;
}
MYSQL_STMT prepare_stmt(MYSQL *conn, char *sql) {
MYSQL_STMT *stmtP = mysql_stmt_init(conn);
if (!stmtP) {
log_to_console("Cannot create statement, out of memory.");
exit(1);
}
MYSQL_STMT stmt = *stmtP;
if (mysql_stmt_prepare(&stmt, sql, strlen(sql))) {
log_to_console("Preparing statement failed: %s", mysql_error(conn));
exit(1);
}
return stmt;
}
void bind_param(MYSQL_BIND *param, enum enum_field_types fieldType, char* buffer, my_bool *isNull, unsigned long *length) {
param->buffer_type = fieldType;
param->buffer = buffer;
param->is_null = isNull;
param->length = length;
}
void bind_string_param(MYSQL_BIND *param, int stringSize, char* buffer, my_bool *isNull, unsigned long *length) {
bind_param(param, MYSQL_TYPE_STRING, buffer, isNull, length);
param->buffer_length = stringSize;
}
void bind_result(MYSQL_BIND *result, enum enum_field_types fieldType, char* buffer, my_bool *isNull, unsigned long *length) {
bind_param(result, fieldType, buffer, isNull, length);
}
void bind_string_result(MYSQL_BIND *result, int stringSize, char* buffer, my_bool *isNull, unsigned long *length) {
bind_string_param(result, stringSize, buffer, isNull, length);
}下面是实际运行查询的代码：
#include "../include/dbutil.h"
int main() {
MYSQL conn = get_connection("localhost", "user", "pass", "test");
MYSQL_STMT stmt = prepare_stmt(&conn, "SELECT hostname from hosts where id = ?");
MYSQL_BIND param[1], result[1];
memset(param, 0, sizeof(param));
memset(result, 0, sizeof(result));
int in = 1;
unsigned long length = 200;
my_bool isNull[2];
isNull[0] = 0;
char out[200];
bind_param(¶m[0], MYSQL_TYPE_LONG, (char *) &in, &isNull[0], (unsigned long *)0);
bind_string_result(&result[0], 200, (char *) &out, &isNull[1], &length);
mysql_stmt_bind_param(&stmt, param);
mysql_stmt_execute(&stmt);
mysql_stmt_bind_result(&stmt, result);
mysql_stmt_store_result(&stmt);
mysql_stmt_fetch(&stmt);
printf("Restult %s\n", out);
mysql_stmt_close(&stmt);
mysql_close(&conn);
return 0;
}语句执行并返回预期的结果，但代码在命中时出现分段错误
mysql_stmt_close(&stmt);我查看了核心转储文件，发现segfault是由libc free()语句引起的，我假定libc free()语句在libmysql.c的free_root()中调用，在
my_bool STDCALL mysql_stmt_close(MYSQL_STMT *stmt)
{
MYSQL *mysql= stmt->mysql;
int rc= 0;
DBUG_ENTER("mysql_stmt_close");
free_root(&stmt->result.alloc, MYF(0));
free_root(&stmt->mem_root, MYF(0));
free_root(&stmt->extension->fields_mem_root, MYF(0));
...具体地说。核心转储说明*stmt.extension是语句关闭的时间。你知道为什么会这样吗？
回答 2
Stack Overflow用户
发布于 2012-10-01 02:00:05
这听起来像是代码/库试图free()一些已经释放的内存。
经过一些谷歌搜索，我发现this link.似乎你应该在调用mysql_stmt_close()之前检查以确保stmt不是NULL。如果stmt已经为空，则库已经清除了它，不需要调用mysql_stmt_close()。
Stack Overflow用户
发布于 2012-10-02 09:41:28
在这里检查out参数：
char out[200];
...
bind_string_result(&result[0], 200, (char *) &out, &isNull[1], &length);如果您看到您的bind_string_result声明：
void bind_string_result(MYSQL_BIND *result, int stringSize, char* buffer, my_bool *isNull, unsigned long *length) {当您发送指向char *的指针时，该函数期望接收char *类型的参数，即char **
由于您将参数强制转换为char *，因此编译器不会给您任何警告，但这可能会在您的内存中产生冲突。试着调用你的函数：
bind_string_result(&result[0], 200, out, &isNull[1], &length);页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/12662868
复制相关文章
相似问题
腾讯云开发者
