Can C achieve Go-style Defer Functionality with Minimal Overhead?

Standard delay/terminator implementation in C

The delay function in Go language is a way to execute a block of code when the function exits Mechanism that simplifies resource cleanup and error handling. This article explores the possibility of a similar deferred implementation in C, and the feasibility of alternatives in existing libraries.

Existing implementations

The C standard library, Boost and other third-party libraries do not yet provide ready-made lazy implementations. However, the following lightweight custom implementation provides similar functionality to the Go language:

<code class="cpp">struct defer_dummy {};
template <class F> struct deferrer { F f; ~deferrer() { f(); } };
template <class F> deferrer<F> operator*(defer_dummy, F f) { return {f}; }
#define DEFER_(LINE) zz_defer##LINE
#define DEFER(LINE) DEFER_(LINE)
#define defer auto DEFER(__LINE__) = defer_dummy{} *[&]()</code>

Usage

This implementation is used in the same way as the Go language Delay syntax is similar:

<code class="cpp">defer {
    // 要在函数退出时执行的代码块
};</code>

Example Usage

<code class="cpp">#include <cstdio>
#include <cstdlib>

bool read_entire_file(char *filename, std::uint8_t *&data_out,
                      std::size_t *size_out = nullptr) {
    auto file = std::fopen(filename, "rb");
    if (!file)
        return false;

    defer { std::fclose(file); }; // 自动关闭文件

    // ...其他文件操作代码

    return true;
}

int main(int argc, char **argv) {
    if (argc < 2)
        return -1;

    std::uint8_t *file_data = nullptr;
    std::size_t file_size = 0;

    auto read_success = read_entire_file(argv[1], file_data, &file_size);

    defer { delete[] file_data; }; // 自动释放文件数据

    if (read_success) {
        // ...文件处理代码

        return 0;
    } else {
        return -1;
    }
}</code>

Advantages

• None Overhead: This implementation introduces no additional overhead, unlike other object or smart pointer based implementations.
• Easy syntax: The syntax mimics the lazy syntax of Go language, making the code clearer and easier to read.
• Zero Dependencies: The implementation is completely self-contained and does not increase compilation time.

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