Hey there! Let's break down why that error is popping up when you try to assign a string literal directly to your char array in C++. This is a super common gotcha for folks moving from C to C++, especially since C++ enforces stricter rules around array handling.

The Core Problem: Array Names Are Non-Modifiable Lvalues #

When you declare char message[sizeArr];, the name message isn't a regular variable you can reassign at will. It acts as a non-modifiable lvalue—think of it as a constant pointer pointing to the first element of your array. When you write message = "I am sending this back";, you're trying to overwrite that fixed pointer with the address of the string literal, which both C and C++ explicitly forbid.

Wait, Did I Do This in C Before? #

Actually, no—you probably confused initialization with assignment! In both languages, this is totally valid (it's initialization):

char message[sizeArr] = "I am sending this back";

Here, the compiler copies the characters of the string literal into your array when it's first created. But splitting declaration and assignment like you did:

char message[sizeArr];
message = "I am sending this back"; // Invalid in C AND C++!

This never was standard-compliant. Some C compilers might let it slide with a warning, but C++ calls it out immediately with the "modifiable lvalue" error to make it clear you're breaking the rules.

How to Fix It #

You've got a few solid options depending on your use case:

• Use initialization instead of assignment: If you can set the string when you declare the array, this is the simplest approach (as shown above).
• Use a string copy function: For cases where you need to update the array after declaration, use strncpy (safer than strcpy to avoid buffer overflows) from the <cstring> header:

  #include <cstring>
  
  int main() {
      char message[sizeArr];
      strncpy(message, "I am sending this back", sizeArr - 1);
      message[sizeArr - 1] = '\0'; // Ensure the string ends with a null character
  }
  

• Switch to std::string (the C++ way): If you're working in C++, using the standard library's std::string is way easier and safer—it supports direct assignment out of the box:

  #include <string>
  
  int main() {
      std::string message;
      message = "I am sending this back"; // Totally valid and hassle-free!
  }
  

内容的提问来源于stack exchange，提问作者Papbad