sql - libpq 如何传递批量数据

Question

我正在尝试将多行传递到测试表，但我无法理解它在 libpq 中究竟是如何完成的。

我找到了我认为需要的用于复制数据的命令，但没有关于如何使用它们的任何示例。 https://www.postgresql.org/docs/8.3/static/libpq-copy.html

这是我想出的代码，但我在 PQputCopyEnd 函数中遇到了段错误。我在这里很迷路，所以任何帮助都会很棒。

/*
 * testlibpq.c
 *
 *      Test the C version of libpq, the PostgreSQL frontend library.
 */
#include <stdio.h>
#include <string>
#include <stdlib.h>
#include <postgresql/libpq-fe.h>

static void exit_nicely(PGconn *conn)
{
    PQfinish(conn);
    exit(1);
}

int main(int argc, char **argv)
{
    const char *conninfo, *errmsg;
    PGconn     *conn;
    PGresult   *res;

    //std::string buffer = "key1\tcol11\tcol12\nley2\tcol21\tcol22";
    std::string buffer = "key1\tcol11\tcol12";


    if (argc > 1)
        conninfo = argv[1];
    else
        conninfo = "dbname=postgres host=129.24.26.136 user=postgres password=postgresUNM";

    /* Make a connection to the database */
    conn = PQconnectdb(conninfo);

    /* Check to see that the backend connection was successfully made */
    if (PQstatus(conn) != CONNECTION_OK)
    {
        fprintf(stderr, "Connection to database failed: %s",
                PQerrorMessage(conn));
        exit_nicely(conn);
    }

    //do stuff here
    res = PQexec(conn, "COPY cplusplustest from STDIN");
    int a = PQputCopyData(conn, buffer.c_str(), buffer.length());

    res = PQexec(conn, "COMMIT");

    int b = PQputCopyEnd(conn, errmsg);

    if (errmsg == NULL)
    {
        printf("worked.\n");
    }

    /* close the connection to the database and cleanup */
    PQfinish(conn);

    return 0;
}

Answer 1

• postgres-8.3 很旧；请考虑更新的版本
• b = PQputCopyEnd(conn, errmsg); 的 errmsg 参数必须设置为 NULL(它是 libpq 的输入，表示客户端已经中止复制) ( the manual 仍然相当模糊，我同意。
• 我删除了 C++。
• COMMIT 应该在 CopyEnd 之后。

---

/*
 * testlibpq.c
 *
 *      Test the C version of libpq, the PostgreSQL frontend library.
 */
#include <stdio.h>
#include <string.h>     // <<--
#include <stdlib.h>

// #include <postgresql/libpq-fe.h> // <<--
#include <libpq-fe.h>

static void exit_nicely(PGconn *conn)
{
    PQfinish(conn);
    exit(1);
}
int main(int argc, char **argv)
{
    const char *conninfo, *errmsg;
    PGconn     *conn;
    PGresult   *res;
    int a,b; // <<--

    char buffer[] = "key1\tcol11\tcol12";

    if (argc > 1)
        conninfo = argv[1];
    else
        conninfo = "dbname=test host=/tmp/ user=postgres";

    /* Make a connection to the database */
    conn = PQconnectdb(conninfo);

    /* Check to see that the backend connection was successfully made */
    if (PQstatus(conn) != CONNECTION_OK)
    {
        fprintf(stderr, "Connection to database failed: %s"
                , PQerrorMessage(conn));
        exit_nicely(conn);
    }

    //do stuff here
    errmsg = NULL;      // << HERE
    res = PQexec(conn, "COPY cplusplustest(key1,col11,col12) from STDIN;");
    a = PQputCopyData(conn, buffer, strlen(buffer) );
    b = PQputCopyEnd(conn, errmsg);

    printf("Res=%p a=%d,b=%d\n", res, a, b);

    if (errmsg )
        printf("Failed:%s\n", errmsg);
    else
        printf("worked.\n");

    res = PQexec(conn, "COMMIT;");      // <<-- HERE

    /* close the connection to the database and cleanup */
    PQfinish(conn);

    return 0;
}