Unable to Determine That Every Element of Cell Array Is Assigned

Issue

您会看到以下消息之一：

Unable to determine that every element of 'y' is assigned before this line.

Unable to determine that every element of 'y' is assigned before exiting the function.

Unable to determine that every element of 'y' is assigned before exiting the recursively called function.

原因

For code generation, before you use a cell array element, you must assign a value to it. When you usecellto create a variable-size cell array, for example,cell(1,n), MATLAB^®assigns an empty matrix to each element. However, for code generation, the elements are unassigned. For code generation, after you usecell要创建一个可变大小的单元格数组，必须在使用单元格数组之前分配单元格数组的所有元素。

The code generator analyzes your code to determine whether all elements are assigned before the first use of the cell array. The code generator detects that all elements are assigned when the code follows this pattern:

功能z = CellVarSize1D(n, j)%#codegenassert(n < 100); x = cell(1,n);fori = 1：n x {i} = i;endz = x{j};end

这是多维单元阵列的模式：

功能Z = Cellassign3d（M，N，P）%#codegenassert(m < 100); assert(n < 100); assert(p < 100); x = cell(m,n,p);fori = 1:mforj =1:nfork = 1:p x{i,j,k} = i+j+k;endendendz = x{m,n,p};end

If the code generator detects that some elements are not assigned, code generation fails. Sometimes, even though your code assigns all elements of the cell array, code generation fails because the analysis does not detect that all elements are assigned.

Here are examples where the code generator is unable to detect that elements are assigned:

Elements are assigned in different loops

。。。x = cell(1,n)fori = 1：5 x {i} = 5;endfori = 6:n x{i} = 7;end。。。

The variable that defines the loop end value is not the same as the variable that defines the cell dimension.
```
。。。x =单元格（1，n）;m = n;fori = 1:m x{i} = 2;end。。。
```

For more information, see通过使用单元格的定义可变大小的单元格数组。

Solution

Try one of these solutions:

使用公认的模式分配元素

If possible, rewrite your code to follow this pattern:

。。。x =单元格（1，n）;fori = 1：n x {i} = i;endz = x{j};。。。

Use`repmat`

Sometimes, you can userepmatto define the variable-size cell array.

考虑定义可变大小单元格数组的代码。它将值1分配给奇数元素，并将值2分配给偶数元素。

功能z = repDefine (n,j)%#codegenassert(n < 100); c =cell(1,n);fori = 1:2:n-1 c{i} = 1;endfori = 2:2:n c{i} = 2;endz = c{j};

Code generation does not allow this code because:

More than one loop assigns the elements.
The loop counter does not increment by 1.

Rewrite the code to first usecell创建一个1 x-2单元格数组，其第一个元素是1，其第二个元素为2。然后，使用repmatto create a variable-size cell array whose element values alternate between 1 and 2.

功能z = repVarSize(n, j)%#codegenassert(n < 100); c = cell(1,2); c{1} = 1; c{2} = 2; c1= repmat(c,1,n); z = c1{j};end

通过使用repmat。使用以下模式：

功能x = emptyVarSizeCellArray x = repmat({'abc'},0,0); coder.varsize('x');end

This code indicates thatxis an empty, variable-size cell array of1x3characters that can be passed into or out of functions.

Use`编码器`

As a last resort, you can use编码器to indicate that the code generator can allocate the memory for your cell array without initializing the memory. For example:

功能z = nulcpyCell(n, j)%#codegenassert(n < 100); c =cell(1,n); c1 = coder.nullcopy(c);fori = 1:4 c1{i} = 1;endfori = 5:n c1{i} = 2;endz = c1{j};end

Use编码器with caution. If you access uninitialized memory, results are unpredictable.