Question

我在SO上可以看到多次对此错误的引用，尽管所有答案似乎都可以解决原始的编译错误，但没有一个可以解释错误的真正含义。

我正在使用g++ -Wall -std=c++11 myfile.cpp编译我的cpp文件，并出现以下错误：

myfile.cpp: In function ‘void GenerateMatrix(uint8_t**, uint8_t)’:
myfile.cpp:32:39: error: invalid types ‘uint8_t {aka unsigned char}[uint8_t {aka unsigned char}]’ for array subscript
    std::cout << ", " << (*matrix)[i][j];

我的代码：

#include <iostream>

//// populates an n x n matrix.
//// @return the matrix 
void GenerateMatrix(uint8_t** matrix, uint8_t n)
{

    *matrix = (uint8_t*)malloc(n * n);

    uint8_t* pc = *matrix;
    for(uint8_t i = 0; i < n; i++)
    {
        for(uint8_t j = 0; j < n; j++)
        {
            *pc++ = i+j;
        }
    }

    for(uint8_t i = 0; i < n; i++)
    {
        for(uint8_t j = 0; j < n; j++)
        {
            std::cout << ", " << (*matrix)[i][j];
        }
        std::cout << "\n";
    }
}


int main()
{
    uint8_t* matrix = nullptr;
    uint8_t n = 10;
    GenerateMatrix(&matrix, n);
    return 0;
}

我尝试在第二个for循环中将i和j更改为int。这给了我一个类似的错误，但是这次投诉是关于invalid types ‘uint8_t {aka unsigned char}[int]’的，但我仍然不明智。

有人可以帮助我理解此错误吗？

Answer 1

void generateMatrix(uint8_t** matrix, uint8_t n)
//                         ^^
{
    (*matrix) // type is uint8_t*
    [i]       // type is uint8_t
    [j];      // ???
}

您实际上所做的等同于：

uint8_t n = 10;
n[12] = 7;   // no index ('subscript'!) applicable to raw unsigned char
             // or with compiler words, the unsigned char is an invalid
             // type for this operation to be applied on...

同一条消息也可能在另一个方向出现：

class C { }; // note that there's no cast operator to some integral type provided!

int array[7];
C c;
array[c]; // just that this time it's the other operand that has invalid type...

错误“数组下标的类型无效...”是什么意思？

1 个答案: