I'm not a C++ programmer, so I need some help with arrays. I need to assign an array of chars to some structure, e.g.
struct myStructure {
char message[4096];
};
string myStr = "hello"; // I need to create {'h', 'e', 'l', 'l', 'o'}
char hello[4096];
hello[4096] = 0;
memcpy(hello, myStr.c_str(), myStr.size());
myStructure mStr;
mStr.message = hello;
I get error: invalid array assignment
Why it doesn't work, if mStr.message and hello have the same data type?
Because you can't assign to arrays -- they're not modifiable l-values. Use strcpy:
#include <string>
struct myStructure
{
char message[4096];
};
int main()
{
std::string myStr = "hello"; // I need to create {'h', 'e', 'l', 'l', 'o'}
myStructure mStr;
strcpy(mStr.message, myStr.c_str());
return 0;
}
And you're also writing off the end of your array, as Kedar already pointed out.
mStr.message and hello in Alex's code are lvalues, because the expressions &mStr.message and &hello are valid. (See section 5.3.1 paragraph 3 in the C++ standard.)
Why it doesn't work, if
mStr.messageandhellohave the same data type?
Because the standard says so. Arrays cannot be assigned, only initialized.
The declaration char hello[4096]; assigns stack space for 4096 chars, indexed from 0 to 4095.
Hence, hello[4096] is invalid.
hello[4096] = 0; with hello[4095] = 0; without changing the essence of what is being asked.You need to use memcpy to copy arrays.
hello[4096] = 0;is wrong. This is one past the last element of the array. Just remove this line.