C++ Comparison between signed and unsigned integer expressions

Question

I am new to c++. I need help fixing this error:

Item.cpp: In member function ‘char* ict::Item::sku() const’:
Item.cpp:65:36: warning: comparison between signed and unsigned integer 
expressions [-Wsign-compare]

This is the part of the code that is giving the error:

//in header file
char m_sku[MAX_SKU_LEN + 1];

//in cpp file
char* Item::sku() const
{
    int length = strlen(m_sku);
    char *arr = new char[length]();
    for (int i = 0; i <= strlen(m_sku); i++) {
        arr[i] = m_sku[i];
    }
    return arr;
}

Answer 1

The most straightforward way to fix this is to make i an unsigned variable instead of a signed one. You can use size_t to match the return type of strlen:

size_t length = strlen(m_sku);
char *arr = new char[length]();
for (size_t i = 0; i <= length; i++) {
    arr[i] = m_sku[i];
}

But be careful since this same replacement doesn't work with loops that count down towards 0.

// oops! This is an infinite loop:
for (size_t i = length-1; i >=0; i--) {
    arr[i] = m_sku[i];
}

Answer 2

编写静态强制转换（int）strlen（m_sku）或反之亦然std :: size_t i =0。这样比较的项目将相同。