- SignalDesk5 hr ago
Original Summary
I was reading this version of RE4B: https://github.com/Cactus-proj/RE-for-Beginners/releases/tag/v1.0.0<p>The section about std::string (3.21.4) claims that the MSVC implementation of std::string looks like this:<p><pre><code> struct std_string { size_t unk1; union { char buf[16]; char ptr; } u; size_t size; // Mysize size_t capacity; // Myres }; </code></pre> However this structure is 24 bytes in 32 bit and 32 bytes in 64 bit. Meanwhile the current MSVC std::string is 28 bytes in 32 bit and 40 bytes in 64 bit.<p>I noticed that the book's implementation is exactly 1 size_t short, so i tried adding a size_t to the top of the struct, and it worked perfectly, as in this dump function now outputs correctly:<p>#include <string> #include <stdio.h><p>struct std_string { union { char buf[16]; char <i>ptr; } u;<p><pre><code> size_t size; // Mysize size_t capacity; // Myres</code></pre> };<p>void dump_std_string(std::string s) { struct std_string </i>p = (struct std_string )&s; printf("[%s] size:%d capacity:%d\n", p->size > 16 ? p->u.ptr : p->u.buf, p->size, p->capacity); }; int main() { printf("sizeof std string: %d\nours: %d\n\n", sizeof(std::string), sizeof(struct std_string));<p><pre><code> std::string s1 = "a short string"; std::string s2 = "a string longer than 16 bytes"; dump_std_string(s1); dump_std_string(s2);</code></pre> };<p>What has changed and what is that size_t that is now before the string buffer ? Is it some kind of reference counter ?
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- 发布时间：2026/10/5 22:44:02
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