GHashTable 对两个相同输入的响应完全不同

Question

以下是我可以创建的最短的可编译演示。

查看接近尾部的 printf 调用，输出如下。我不知道为什么两个完全相同的语句可以做到这一点。它可能与输入类型有关，但我看不出它可能是什么。

#include <gtk/gtk.h>
#include <libxml/xmlmemory.h>
#include <libxml/parser.h>
int
main (int argc, char *argv[])
{
    gtk_init (&argc, &argv);
    GtkBuilder * builder = gtk_builder_new ();
    GHashTable * table = g_hash_table_new(NULL,NULL);
    int i;
    char builderdoc[] = "<?xml version=\"1.0\"?>"
"<interface>"
"  <requires lib=\"gtk+\" version=\"2.16\"/>"
 " <!-- interface-naming-policy project-wide -->"
"  <object class=\"GtkCheckButton\" id=\"checkbutton1\">"
"  </object>"
"</interface>";

    // Load gtkbuilder
    gtk_builder_add_from_string (builder, builderdoc, sizeof(builderdoc),NULL);

    char * buffer[][2] = {
    {"log","checkbutton1"}
    };

    // Load array of widgets into hash table (Shortened)
    for(i = 0; i < sizeof(buffer) / sizeof(char *) / 2; i++){
        g_hash_table_insert(table,(gchar *) buffer[i][0],gtk_builder_get_object (builder, (gchar *) buffer[i][1]));
    }


    // Load xml doc
    xmlDocPtr doc;
    xmlNodePtr cur;
    xmlNodePtr cur2;
    char xmldoc[] = "<?xml version=\"1.0\"?>"
                    "<CsSettings>"
                    "<options>"
                    "<check name=\"log\" value=\"1\" />"
                    "</options>"
                    "</CsSettings>";

    doc = xmlParseMemory(xmldoc, (int) sizeof(xmldoc));
    cur = xmlDocGetRootElement(doc);
    cur = cur->xmlChildrenNode;

    // Find what we're looking for
    while (cur != NULL){
        if(xmlStrEqual(cur->name, (xmlChar *) "options")){
            cur2 = cur->xmlChildrenNode;
            while (cur2 != NULL){
                if(xmlStrEqual(cur2->name, (xmlChar *) "check")){
                    // We've found it, now print some output
                    printf("Plain old lookup: g_hash_table_lookup(table,\"log\"): %p\n",g_hash_table_lookup(table,"log"));
                    printf("Variable lookup : g_hash_table_lookup(table,\"%s\"): %p\n",(gchar *) xmlGetProp(cur2, (xmlChar *) "name"),g_hash_table_lookup(table,(gchar *) xmlGetProp(cur2, (xmlChar *) "name")));
                    printf("Xml says we should lookup: '%s'\n",(gchar *) xmlGetProp(cur2, (xmlChar *) "name"));

                }
                cur2 = cur2->next;
            }
        }       
        cur = cur->next;
    }

}

以及令人困惑的输出：

Plain old lookup: g_hash_table_lookup(table,"log"): 0x1e369a0
Variable lookup : g_hash_table_lookup(table,"log"): (nil)
Xml says we should lookup: 'log'

Answer 1

您可能会从哈希表中得到意外的行为，因为您没有在构造函数上设置任何哈希或相等函数，在这种情况下，使用 g_direct_hash() 和 g_direct_equal( 在指针上直接进行哈希处理) 函数适用。

如果表的键是 gchar * 我会使用 g_str_hash 和 g_str_equal。像这样初始化你的表：

GHashTable * table = g_hash_table_new(g_str_hash,g_str_equal);

如果哈希表的键是要存储的内容，那么直接对指针进行哈希不是一个好主意指针所指的是。请告诉我们这是否可以解决问题。