Question

我编写了一个步步高位置评估系统，我尝试使用指定的初始化器，复合文字和可变参数宏来创建关键字参数函数，如描述here，并在Ben Klemens＆＃39;优秀的书 21st Century C 。

// from board.h
typedef struct _board_t board_t;  

// from evaluator.h (evaluator is an "interface" in a primitive object system.)
#define EVALUATOR(v) (evaluator_t*)(v)

enum { OUTPUT_WIN, OUTPUT_WINGAMMON, OUTPUT_WINBACKGAMMON,
       OUTPUT_LOSEGAMMON, OUTPUT_LOSEBACKGAMMON, N_OUTPUT };

typedef struct _evaluator_t evaluator_t;

// from composite_evaluator.h
#define N_MAX_EVALUATORS_IN_COMPOSITE 10

typedef evaluator_t * (*new_func)( void *d );

typedef struct {
    int n_eval;
    int (*classifier)( const board_t *b );
    struct {
        new_func construct;
        void *args;
    } config[N_MAX_EVALUATORS_IN_COMPOSITE];
} composite_evaluator_config_t;

// some evaluator implementations (just decl for _new)
typedef struct _overevaluator_t       overevaluator_t;
typedef struct _onesidebearoff_t      onesidebearoff_t;
typedef struct _neuralnet_evaluator_t neuralnet_evaluator_t;
overevaluator_t        *overevaluator_new       (void *args);
onesidebearoff_t       *onesidebearoff_new      (void *args);
neuralnet_evaluator_t  *neuralnet_evaluator_new (void *args);

// and a classifing function decl.
int classify_position( const board_t *b );

// Example from main program
#include <stdio.h>
int main()
{
    // This is of course coded in a variadic macro, but the macro is left out for simplicity of the example.
    composite_evaluator_config_t myeval = {
        .n_eval = 5,
        .classifier = classify_position,
        .config = {
          [0] = { .construct = (new_func)overevaluator_new },
          [1] = { .construct = (new_func)onesidebearoff_new },
          [2] = { .construct = (new_func)neuralnet_evaluator_new, .args = &((char*[]){"race.weights", "race", "race"}) },
          [3] = { .construct = (new_func)neuralnet_evaluator_new, .args = &((char*[]){"contact.weights", "contact", "contact"}) },
          [4] = { .construct = (new_func)neuralnet_evaluator_new, .args = &((char*[]){"crashed.weights", "crashed", "contact"}) },
          // The following line is added by a __VA_ARGS__, hence overriding the [3] above.
          [3] = { .construct = (new_func)neuralnet_evaluator_new, .args = &((char*[]){"td1228.weights", "contact", "contact"}) },
        }
    };

    char **args = (char**) myeval.config[3].args; 
    printf("Neural network weights read from '%s'.\n", args[0]);

    return 0;
}

我认为这是合法的C99（？），但是当我使用GCC（4.9.2 20141224）进行编译时，我收到以下警告：

$ gcc -Wall -Wextra -Wno-override-init -c evaltest.c
evaltest.c: In function ‘main’:
evaltest.c:63:13: warning: initialized field with side-effects overwritten
         [3] = { .construct = (new_func)neuralnet_evaluator_new, .args = &((char*[]){"td1228.weights", "contact", "contact"}) },
         ^
evaltest.c:63:13: warning: (near initialization for ‘myeval.config[3]’)

然而，当我用clang编译时，就像这样：

clang -Wall -Wextra -Wno-initializer-overrides -c evaltest.c

我完全没有警告！然而，两个编译器似乎都构建了预期的代码。

所以，clang和我认为这是好的代码。有人可以解释为什么GCC发给我这个警告吗？警告有效吗？我能以任何方式压制它吗？或者它是GCC的错误？

Answer 1

因为这里

[3] = { .construct = (new_func)neuralnet_evaluator_new, .args = &((char*[]){"td1228.weights", "contact", "contact"}) }

你已经.config[3]两次

Gcc 4.9 Doc: Designated-Init

如果多次初始化相同的字段，则它具有上次初始化的值。如果任何此类重写的初始化具有副作用，则未指定副作用是否发生。目前，GCC丢弃它们并发出警告。

初始化复杂结构，GCC警告：初始化字段，副作用被覆盖

1 个答案: