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我正在使用uthash.h来存储我的应用程序的配置。由于配置来自运行时读取的文件,因此哈希中的键和值都是动态分配char *的:

typedef struct config_entry {
    char *name;
    char *value;
    UT_hash_handle hh;
} CONFIG_ENTRY;

正如用户指南中所解释的,我实现了自己的函数来向 config-hash 添加键以确保唯一性。这里是:

void cfg_put( char *name, char *value, FREE_FLAGS flags ) {

    CONFIG_ENTRY *entry;

    //first, check if the key is already in the hash
    HASH_FIND_STR( config_, name, entry );
    if( entry == NULL ) {
        //key doesn't exist yet => create new one
        entry = (CONFIG_ENTRY *)malloc( sizeof( CONFIG_ENTRY ) );
        entry->name = name;
        HASH_ADD_KEYPTR( hh, config_, entry->name, strlen(entry->name), entry );
    } else {
        //key exists => possibly free existing pointers before setting value

        if( (flags & FREE_NAME) == FREE_NAME ) {        //
            free( entry->name );                        // these lines seem to be
        }                                               // problematic.
        entry->name = name;                             //

        if( (flags & FREE_VALUE) == FREE_VALUE ) {
            free( entry->value );
        }
    }

    //Finally, set the value
    entry->value = value;
}

我还写了一些测试用例来检查我的实现,它们似乎运行得很好。但是,如果我使用 valgrind 运行测试来检查 memleaks,我总是会得到以下信息:

==2561== Invalid read of size 1
==2561==    at 0x4026097: bcmp (mc_replace_strmem.c:541)
==2561==    by 0x804ADF5: cfg_get (in /home/gj/..../test/config_test)
==2561==    by 0x804B2C7: test_config1 (in /home/..../test/config_test)
==2561==    by 0x402E446: run_single_test (in /usr/local/lib/libcunit.so.1.0.1)
[...]
==2561==  Address 0x4194210 is 0 bytes inside a block of size 4 free'd
==2561==    at 0x4023B6A: free (vg_replace_malloc.c:366)
==2561==    by 0x804A872: cfg_put (in /home/..../test/config_test)
==2561==    by 0x804B27D: test_config1 (in /home/..../test/config_test)
==2561==    by 0x402E446: run_single_test (in /usr/local/lib/libcunit.so.1.0.1)
[...]

这是测试用例和完整性的实现cfg_get

void test_config1( void ) {

    cfg_clear( FREE_ALL );

    cfg_put( strdup("foo"), "bar", FREE_NONE );
    CU_ASSERT_EQUAL( cfg_count(), 1 );
    CU_ASSERT_STRING_EQUAL( cfg_get("foo"), "bar" );

    cfg_dump();

    cfg_put( "foo", "baz", FREE_NAME );
    CU_ASSERT_EQUAL( cfg_count(), 2 );
    CU_ASSERT_STRING_EQUAL( cfg_get("foo"), "baz" );

    cfg_clear( FREE_NONE );

    cfg_dump();
}

cfg_get

char *cfg_get( const char *name ) {

    CONFIG_ENTRY *entry = NULL;
    HASH_FIND_STR( config_, name, entry );

    if( entry ) {
        return entry->value;
    } else {
        return NULL;
    }
}

不知何故,似乎我在将旧name指针cfg_get覆盖在cfg_put. 问题只出现在 中name,而不出现在 中value。我太愚蠢了,无法弄清楚,谢谢任何建议。

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2 回答 2

0

您必须提供完整的程序——即重现 valgrind 问题的完整最小示例。您在问题中发布的代码看起来不错,因此该错误必须隐藏在其他地方;例如在cfg_clear()or的代码中cfg_count()

(最初我认为那cfg_count()一定是return HASH_COUNT(config_);——但是那个实现不会通过你的测试用例,所以你必须做一些更奇怪的事情。这意味着cfg_count无论如何该函数的名称可能是错误的。)


从风格上讲,如果避免使用config_全局变量(要求用户自行跟踪FREE_NAMEFREE_VALUE等。也就是说,而不是

typedef struct config_entry {
    char *name;
    char *value;
    UT_hash_handle hh;
} CONFIG_ENTRY;

void cfg_put(char *name, char *value, FREE_FLAGS flags);
void cfg_clear(FREE_FLAGS flags);

你应该只提供

typedef struct config_entry {
    char *name;
    char *value;
    UT_hash_handle hh;
    bool must_free_name;
    bool must_free_value;
} CONFIG_ENTRY;

void cfg_put(char *name, char *value, FREE_FLAGS flags);
void cfg_clear(void);

此时您的测试用例变得更易于管理

void test_config1()
{
    cfg_clear();  // use the stored bits to figure out what needs freeing
    cfg_put(strdup("foo"), "bar", FREE_NAME);  // name is alloc'ed, so name must be freed later
    CU_ASSERT_EQUAL( cfg_count(), 1 );
    CU_ASSERT_STRING_EQUAL( cfg_get("foo"), "bar" );

    cfg_put("foo", "baz", FREE_NONE);  // neither name nor value is alloc'ed
    CU_ASSERT_EQUAL( cfg_count(), 2 );
    CU_ASSERT_STRING_EQUAL( cfg_get("foo"), "baz" );
}
于 2017-02-24T21:58:23.790 回答
0

您的函数存在问题config_put():它修改了已插入哈希的项目的键。你不应该这样做。将指针更改为name指向同一个字符串的指针可能是可以的,但可能不是,实现uthash.h有点模糊。

我建议您更改 API,以便config_put()所有字符串管理都进行,让哈希拥有所有字符串,config_并且不再调用strdup(). test_config1这要简单得多,并且避免了在哈希结构之外对字符串值的生命周期进行潜在的复杂且容易出错的跟踪:

void cfg_put(const char *name, const char *value) {

    CONFIG_ENTRY *entry;

    //first, check if the key is already in the hash
    HASH_FIND_STR(config_, name, entry);
    if (entry == NULL) {
        //key doesn't exist yet => create new one
        entry = malloc(sizeof(*entry));
        entry->name = strdup(name);
        HASH_ADD_KEYPTR(hh, config_, entry->name, strlen(entry->name), entry );
    } else {
        //key exists => free existing value pointer if any
        free(entry->value);
    }

    //Finally, set the value
    entry->value = value ? strdup(value) : NULL;
}
于 2017-02-24T22:43:07.557 回答