为什么MySQL会破坏wget_iri_relative_to_abs？

Question

考虑下面的复制器：

#include <wget.h>
#include <string.h>
#include <mysql.h>

MYSQL *mysql_con;

void
mysql_stop()
{
        mysql_close(mysql_con);
}

void
mysql_start()
{
        mysql_con = mysql_init(NULL);
        if (mysql_con == NULL)
        {
                fprintf(stderr, "%s\n", mysql_error(mysql_con));
                exit(1);
        }
        if (mysql_real_connect(mysql_con, "localhost", "crawler", "password", "crawl", 0, NULL, 0) == NULL)
        {
                fprintf(stderr, "%s\n", mysql_error(mysql_con));
                exit(EXIT_FAILURE);
        }
}

const char * parseURI (char *base_url, char *url)
{
    wget_iri *base = wget_iri_parse(base_url, NULL);
    wget_buffer *buf = wget_buffer_alloc(8192);
    const char *uri = wget_iri_relative_to_abs(base, url, strlen(url), buf);
    wget_buffer_free(&buf);
    wget_iri_free(&base);
    return uri;
}

void crawler_init()
{
    const char *url2 = parseURI("http://www.google.com/", "/intl/en/policies/privacy/");
    printf("%s\n", url2);
}

int main (int argc, char **argv)
{
    const char *url2 = parseURI("http://www.google.com/", "/intl/en/policies/privacy/");
    printf("%s\n", url2);
    mysql_start();
    crawler_init();
    mysql_stop();
}

运行此程序的输出为：

http://www.google.com/intl/en/policies/privacy/
��7�

main中的第一个printf如预期的那样打印出绝对url。crawler_init中的第二个printf输出的是垃圾，而不是相同的绝对url。

这似乎与mysql_real_connect有关，因为当此调用被注释掉时，crawler_init中的第二个printf会打印出预期的绝对url。

为什么？

Answer 1

添加buf->data = NULL;可以解决此问题：

#include <wget.h>
#include <string.h>
#include <mysql.h>

MYSQL *mysql_con;

void
mysql_stop()
{
        mysql_close(mysql_con);
}

void
mysql_start()
{
        mysql_con = mysql_init(NULL);
        if (mysql_con == NULL)
        {
                fprintf(stderr, "%s\n", mysql_error(mysql_con));
                exit(1);
        }
        if (mysql_real_connect(mysql_con, "localhost", "crawler", "1q2w3e4r", "crawl", 0, NULL, 0) == NULL)
        {
                fprintf(stderr, "%s\n", mysql_error(mysql_con));
                exit(EXIT_FAILURE);
        }
}

const char * parseURI (char *base_url, char *url)
{
    wget_iri *base = wget_iri_parse(base_url, NULL);
    wget_buffer *buf = wget_buffer_alloc(8192);
    const char *uri = wget_iri_relative_to_abs(base, url, strlen(url), buf);
    buf->data = NULL;
    wget_buffer_free(&buf);
    wget_iri_free(&base);
    return uri;
}

void crawler_init()
{
    const char *url2 = parseURI("http://www.google.com/", "/intl/en/policies/privacy/");
    printf("%s\n", url2);
}

int main (int argc, char **argv)
{
    const char *url2 = parseURI("http://www.google.com/", "/intl/en/policies/privacy/");
    printf("%s\n", url2);
    mysql_start();
    crawler_init();
    mysql_stop();
}