sqlite3-free（zerrmsg）

SQLite3-free，通常指的是SQLite3的一个免费版本或者是一个开源的库，其中包含了错误处理相关的zerrmsg组件。SQLite是一个轻量级的关系型数据库管理系统，以其嵌入式性质和小型而著名。zerrmsg可能是指SQLite中的错误信息处理模块，它提供了一种机制来处理和格式化数据库操作中可能出现的各种错误代码，并将这些错误信息以人类可读的形式返回。

当你使用SQLite3进行数据库操作时，如果遇到错误，SQLite3-free（或包含zerrmsg的版本）可以帮助你理解发生了什么问题，这对于调试和错误排查非常有用。

相关问题

#include <stdio.h> #include "sqlite3.h" static int callback(void* NotUsed, int argc, char** argv, char** azColName) { int i; for (i = 0; i < argc; i++) { printf("%s = %s\n", azColName[i], argv[i] ? argv[i] : "NULL"); } printf("\n"); return 0; } int main(int argc, char** argv) { sqlite3* db; char* zErrMsg = 0; int rc; char* dbfile = "test.db"; char* sql; rc = sqlite3_open(dbfile, &db); if (rc) { fprintf(stderr, "Can't open database: %s\n", sqlite3_errmsg(db)); sqlite3_close(db); return -1; } //在数据库中创建一个名为person的表 sql = "create table person(id int primary key,first_name text,last_name text);"; rc = sqlite3_exec(db, sql, callback, 0, &zErrMsg); if (rc != SQLITE_OK) { fprintf(stderr, "SQL error: %s\n", zErrMsg); sqlite3_free(zErrMsg); } sql = "insert into person values (1,'zhang','san');" "insert into person values (2,'li','si');" "insert into person values (3,'wang','wu');" "insert into person values (4,'zhao','liu');" "insert into person values (5,'sun','qi');"; rc = sqlite3_exec(db, sql, callback, 0, &zErrMsg); if (rc != SQLITE_OK) { fprintf(stderr, "SQL error: %s\n", zErrMsg); sqlite3_free(zErrMsg); } sql = "select * from person where id=3;"; rc = sqlite3_exec(db, sql, callback, 0, &zErrMsg); if (rc != SQLITE_OK) { fprintf(stderr, "Failed to select data: %s\n", zErrMsg); sqlite3_free(zErrMsg); } sql = "delete from person where id=5;"; rc = sqlite3_exec(db, sql, callback, 0, &zErrMsg); if (rc != SQLITE_OK) { fprintf(stderr, "Failed to delete data: %s\n", zErrMsg); sqlite3_free(zErrMsg); } sql = "select * from person;"; rc = sqlite3_exec(db, sql, callback, 0, &zErrMsg); if (rc != SQLITE_OK) { fprintf(stderr, "SQL error: %s\n", zErrMsg); sqlite3_free(zErrMsg); } sqlite3_close(db); return 0; }添加注释

//引入头文件
#include <stdio.h>
#include "sqlite3.h"

//回调函数
static int callback(void* NotUsed, int argc, char** argv, char** azColName) {
int i;
for (i = 0; i < argc; i++) {
printf("%s = %s\n", azColName[i], argv[i] ? argv[i] : "NULL");
}
printf("\n");
return 0;
}

//主函数
int main(int argc, char** argv) {
sqlite3* db;
char* zErrMsg = 0;
int rc;
char* dbfile = "test.db";
char* sql;
rc = sqlite3_open(dbfile, &db); //连接数据库
if (rc) {
fprintf(stderr, "Can't open database: %s\n", sqlite3_errmsg(db));
sqlite3_close(db);
return -1;
}
sql = "create table person(id int primary key,first_name text,last_name text);";
rc = sqlite3_exec(db, sql, callback, 0, &zErrMsg); //创建表
if (rc != SQLITE_OK) {
fprintf(stderr, "SQL error: %s\n", zErrMsg);
sqlite3_free(zErrMsg);
}
sql = "insert into person values (1,'zhang','san');" "insert into person values (2,'li','si');" "insert into person values (3,'wang','wu');" "insert into person values (4,'zhao','liu');" "insert into person values (5,'sun','qi');";
rc = sqlite3_exec(db, sql, callback, 0, &zErrMsg); //插入数据
if (rc != SQLITE_OK) {
fprintf(stderr, "SQL error: %s\n", zErrMsg);
sqlite3_free(zErrMsg);
}
sql = "select * from person where id=3;";
rc = sqlite3_exec(db, sql, callback, 0, &zErrMsg); //查询数据
if (rc != SQLITE_OK) {
fprintf(stderr, "Failed to select data: %s\n", zErrMsg);
sqlite3_free(zErrMsg);
}
sql = "delete from person where id=5;";
rc = sqlite3_exec(db, sql, callback, 0, &zErrMsg); //删除数据
if (rc != SQLITE_OK) {
fprintf(stderr, "Failed to delete data: %s\n", zErrMsg);
sqlite3_free(zErrMsg);
}
sql = "select * from person;";
rc = sqlite3_exec(db, sql, callback, 0, &zErrMsg); //查询数据
if (rc != SQLITE_OK) {
fprintf(stderr, "SQL error: %s\n", zErrMsg);
sqlite3_free(zErrMsg);
}
sqlite3_close(db); //关闭数据库连接
return 0;
}

sqlcmd = "insert into user values (5,'sun','qi');"; rc = sqlite3_exec(db, sqlcmd, callback, 0, &zErrMsg); if (rc != SQLITE_OK) { fprintf(stderr, "SQL error: %s\n", zErrMsg); sqlite3_free(zErrMsg); }解释这段代码的意思并添加注释

这段代码使用 SQLite 数据库 API 向名为 "user" 的表中插入了一行数据。下面是每行代码的注释：

sqlcmd = "insert into user values (5,'sun','qi');";  // 定义 SQL 插入语句
rc = sqlite3_exec(db, sqlcmd, callback, 0, &zErrMsg);  // 执行 SQL 语句，并将结果传递到回调函数中
if (rc != SQLITE_OK) {  // 如果返回结果不为 SQLITE_OK，则说明执行 SQL 语句出现了错误
    fprintf(stderr, "SQL error: %s\n", zErrMsg);  // 将错误信息打印到标准错误输出流中
    sqlite3_free(zErrMsg);  // 释放错误信息的内存
}

这段代码中的 SQL 语句是 "insert into user values (5,'sun','qi');"，它的作用是向 "user" 表中插入一行数据，该行数据包含三个字段，分别是 "5"、"sun" 和 "qi"。如果执行 SQL 语句出现了错误，将会通过标准错误输出流打印错误信息。