为目标 C 静态数组动态分配长度

发布于 2024-12-06 08:39:40 字数 957 浏览 5 评论 0原文

您好，我对 iOS 编程和使用 Objective C 比较陌生。最近我遇到了一个似乎无法解决的问题，我正在编写一个 OBJ 模型加载器以在我的 iOS 编程中使用。为此，我使用两个数组，如下所示：

static CGFloat modelVertices[360*9]={};
static CGFloat modelColours[360*12]={};

可以看出，当前使用硬编码值 360（特定模型中的面数）分配长度。有没有办法可以从读取 OBJ 文件后计算出的值动态分配该值，如下所示？

int numOfVertices = //whatever this is read from file;
static CGFloat modelColours[numOfVertices*12]={};

我尝试过使用 NSMutable 数组，但发现这些数组很难使用，因为在实际绘制收集的网格时，我需要使用以下代码：

-(void)render
{
// load arrays into the engine
glVertexPointer(vertexStride, GL_FLOAT, 0, vertexes);
glEnableClientState(GL_VERTEX_ARRAY);
glColorPointer(colorStride, GL_FLOAT, 0, colors);   
glEnableClientState(GL_COLOR_ARRAY);

//render
glDrawArrays(renderStyle, 0, vertexCount);  
}

如您所见，命令 glVertexPointer 需要将值作为 CGFloat 数组：

glVertexPointer (GLint size, GLenum type, GLsizei stride, const GLvoid *pointer);

原文

Hi I am relatively new to programming on iOS and using objective C. Recently I have come across an issue I cannot seem to solve, I am writing a OBJ model loader to use within my iOS programming. For this I use two arrays as below:

static CGFloat modelVertices[360*9]={};
static CGFloat modelColours[360*12]={};

As can be seen the length is currently allocated with a hard coded value of 360 (the number of faces in a particular model). Is there no way this can be dynamically allocated from a value that has been calculated after reading the OBJ file as is done below?

int numOfVertices = //whatever this is read from file;
static CGFloat modelColours[numOfVertices*12]={};

I have tried using NSMutable arrays but found these difficult to use as when it comes to actually drawing the mesh gathered I need to use this code:

-(void)render
{
// load arrays into the engine
glVertexPointer(vertexStride, GL_FLOAT, 0, vertexes);
glEnableClientState(GL_VERTEX_ARRAY);
glColorPointer(colorStride, GL_FLOAT, 0, colors);   
glEnableClientState(GL_COLOR_ARRAY);

//render
glDrawArrays(renderStyle, 0, vertexCount);  
}

As you can see the command glVertexPointer requires the values as a CGFloat array:

glVertexPointer (GLint size, GLenum type, GLsizei stride, const GLvoid *pointer);

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誰認得朕 2024-12-13 08:39:40

您可以使用 C 风格的 malloc 为数组动态分配空间。

int numOfVertices = //whatever this is read from file;
CGFloat *modelColours = (CGFloat *) malloc(sizeof(CGFloat) * numOfVertices);

You could use a c-style malloc to dynamically allocate space for the array.

int numOfVertices = //whatever this is read from file;
CGFloat *modelColours = (CGFloat *) malloc(sizeof(CGFloat) * numOfVertices);

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她比我温柔 2024-12-13 08:39:40

当声明静态变量时，必须在编译时知道其大小和初始值。您可以做的是将变量声明为指针而不是数组，使用malloc或calloc为数组分配空间并将结果存储在变量中。

static CGFloat *modelColours = NULL;

int numOfVertices = //whatever this is read from file;
if(modelColours == NULL) {
    modelColours = (CGFloat *)calloc(sizeof(CGFloat),numOfVertices*12);
}

我在这里使用了calloc而不是malloc，因为静态数组默认会用0填充，这样可以确保代码的一致性。

When you declare a static variable, its size and initial value must be known at compile time. What you can do is declare the variable as a pointer instead of an array, the use malloc or calloc to allocate space for the array and store the result in your variable.

static CGFloat *modelColours = NULL;

int numOfVertices = //whatever this is read from file;
if(modelColours == NULL) {
    modelColours = (CGFloat *)calloc(sizeof(CGFloat),numOfVertices*12);
}

I used calloc instead of malloc here because a static array would be filled with 0s by default, and this would ensure that the code was consistent.

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