c - 将 char 转换为 wchar_t 的问题(长度错误)

Question

我正在尝试创建一个简单的数据结构，它可以轻松地在 ASCII 字符串和 Unicode 字符串之间来回转换。我的问题是函数 mbstowcs 返回的长度是正确的，但函数 wcslen 在新创建的 wchar_t 字符串上返回的长度不正确。我在这里错过了什么吗？

typedef struct{

    wchar_t *string;
    long length; // I have also tried int, and size_t
} String;

void setCString(String *obj, char *str){

    obj->length = strlen(str);

    free(obj->string); // Free original string
    obj->string = (wchar_t *)malloc((obj->length + 1) * sizeof(wchar_t)); //Allocate space for new string to be copied to

    //memset(obj->string,'\0',(obj->length + 1)); NOTE: I tried this but it doesn't make any difference

    size_t length = 0;

    length = mbstowcs(obj->string, (const char *)str, obj->length);

    printf("Length = %d\n",(int)length); // Prints correct length
    printf("!C string %s converted to wchar string %ls\n",str,obj->string); //obj->string is of a wcslen size larger than Length above...

    if(length != wcslen(obj->string))
            printf("Length failure!\n");

    if(length == -1)
    {
        //Conversion failed, set string to NULL terminated character
        free(obj->string);
        obj->string = (wchar_t *)malloc(sizeof(wchar_t));
        obj->string = L'\0';
    }
    else
    {
        //Conversion worked! but wcslen (and printf("%ls)) show the string is actually larger than length
        //do stuff
    }
}

Answer 1

您需要传递给 mbstowcs() 的长度包括 L'\0'终止符，但您在 obj->length() 中计算出的长度不包括它 - 您需要在传递给 mbstowcs() 的值上加 1 .

另外，不要使用strlen(str)要确定转换后的字符串的长度，您应该使用 mbstowcs(0, src, 0) + 1 .您还应该更改 str 的类型至 const char * ，并省略类型转换。 realloc()可以用来代替 free() / malloc()一对。总的来说，它应该是这样的:

typedef struct {
    wchar_t *string;
    size_t length;
} String;

void setCString(String *obj, const char *str)
{
    obj->length = mbstowcs(0, src, 0);
    obj->string = realloc(obj->string, (obj->length + 1) * sizeof(wchar_t)); 

    size_t length = mbstowcs(obj->string, str, obj->length + 1);

    printf("Length = %zu\n", length);
    printf("!C string %s converted to wchar string %ls\n", str, obj->string);

    if (length != wcslen(obj->string))
            printf("Length failure!\n");

    if (length == (size_t)-1)
    {
        //Conversion failed, set string to NULL terminated character
        obj->string = realloc(obj->string, sizeof(wchar_t));
        obj->string = L'\0';
    }
    else
    {
        //Conversion worked!
        //do stuff
    }
}

Mark Benningfield 指出 mbstowcs(0, src, 0)是 C 标准的 POSIX/XSI 扩展 - 要仅在标准 C 下获得所需的长度，您必须改为使用:

    const char *src_copy = src;
    obj->length = mbstowcs(NULL, &src_copy, 0, NULL);