Cpp

string memory layout

source

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// string.cpp
#include <string>
#include <iostream>

void func(std::string &hello) {
    std::cout << hello.size();
    std::cout << hello.capacity();
}

int main () {
    std::string hello{"hello, world!!!"};
    hello += "this is a test";
    func(hello);
    std::cout << "Program end\n";
    return 0;
}

/*
enum { _S_local_capacity = 15 / sizeof(_CharT) };
      union
      {
	_CharT           _M_local_buf[_S_local_capacity + 1];
	size_type        _M_allocated_capacity;
      };

## std::sting: memory size:
sizeof(std::string) = 32
*/

debug

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> g++ -O1 string.cpp -o string
> gdb string

(gdb) br func
Breakpoint 1 at 0x1249
(gdb) run

(gdb) x /4gx $rdi
0x7fffffffda90: 0x000055555556aeb0      0x000000000000001d
0x7fffffffdaa0: 0x000000000000001e      0x00212121646c726f
(gdb) x /s 0x000055555556aeb0
0x55555556aeb0: "hello, world!!!this is a test"

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