在 memset 之后未寫入結構數組的值

Question

我編寫了一個程序，將值寫入 c 中的結構數組，但似乎沒有任何值寫入結構數組。

在第一個代碼塊中，我實例化了一個結構數組並將該位置的 memory 設置為 0：

struct s_prob prob_values[(int) pow(n, 2)];
memset(prob_values, 0, sizeof(prob_values));

我在 main 之前聲明的 struct s_prob 如下：

struct s_prob {
    int index;
    float probability;
    unsigned long count;
};

我用來將值寫入結構數組的代碼如下：

int prob_count = 0;
for (int i = 0; i < n; i++) {
    for (int j = 0; j < n; j++) {
        printf("%d, %d, ", prob_count, prob_values[prob_count].index);
        prob_values[prob_count].index = (int) prob_count;
        prob_values[prob_count].probability = (float) pow((1.0 - p_x_error), n - i) * pow((1.0 - p_z_error), num_data_qubits - j) * pow(p_x_error, i) * pow(p_z_error, j);
        prob_values[prob_count].count = (unsigned long) pascal_triangle[n][i+j];
        prob_count++;
        printf("At index %d: prob: %e, count: %lu\n", prob_values[prob_count].index, prob_values[prob_count].probability, prob_values[prob_count].count);
    }
}

第一個打印語句的格式是這樣的，因為我想將索引的值與計數器進行比較以確保它們相同。 這是因為第二個 print 語句打印的值根本不是調用 memset 之前應該有的值。 現在，根本沒有寫入任何值。

這是我在實施 memset 之前收到的 output：

0, 713, At index 0: prob: 0.000000e+00, count: 456
1, 0, At index 0: prob: 0.000000e+00, count: 0
2, 0, At index -890830848: prob: 6.235778e-43, count: 1914664608552
3, -890830848, At index 0: prob: 0.000000e+00, count: 0
4, 0, At index 0: prob: 0.000000e+00, count: 4112
5, 0, At index 0: prob: 0.000000e+00, count: 1914664608560
6, 0, At index 0: prob: 0.000000e+00, count: 1914664591506
7, 0, At index -890805472: prob: 6.235778e-43, count: 3372220617
8, -890805472, At index 0: prob: 0.000000e+00, count: 0
9, 0, At index -890830512: prob: 6.235778e-43, count: 0
10, -890830512, At index 73: prob: 0.000000e+00, count: 1023
11, 73, At index -890805472: prob: 6.235778e-43, count: 2533359767
12, -890805472, At index 201: prob: 0.000000e+00, count: 0
13, 201, At index 0: prob: 0.000000e+00, count: 0
14, 0, At index 0: prob: 0.000000e+00, count: 257
15, 0, At index 8: prob: 0.000000e+00, count: 0
16, 8, At index 4112: prob: 0.000000e+00, count: 4096
17, 4112, At index 2: prob: 0.000000e+00, count: 1914664583168
18, 2, At index 129: prob: 0.000000e+00, count: 140727915623501
19, 129, At index -890830848: prob: 6.235778e-43, count: 10
20, -890830848, At index 4096: prob: 0.000000e+00, count: 0
21, 4096, At index -890819760: prob: 6.235778e-43, count: 105920832884
22, -890819760, At index 0: prob: 4.203895e-45, count: 0
23, 0, At index 0: prob: 0.000000e+00, count: 4112
24, 0, At index 0: prob: 0.000000e+00, count: 0
25, 0, At index 0: prob: 0.000000e+00, count: 1914664591506
26, 0, At index 0: prob: 0.000000e+00, count: 3405775306
27, 0, At index 0: prob: 0.000000e+00, count: 2533359767
28, 0, At index 0: prob: 0.000000e+00, count: 0
29, 0, At index 0: prob: 0.000000e+00, count: 0
30, 0, At index 0: prob: 0.000000e+00, count: 2533359767
31, 0, At index 0: prob: 0.000000e+00, count: 0
32, 0, At index 4: prob: 0.000000e+00, count: 4294967295
33, 4, At index -919681840: prob: 4.590514e-41, count: 105920833784
34, -919681840, At index 0: prob: 0.000000e+00, count: 4096
35, 0, At index 1: prob: 0.000000e+00, count: 140727914045745
36, 1, At index 0: prob: 0.000000e+00, count: 4096
37, 0, At index 129: prob: 0.000000e+00, count: 140727915577344
38, 129, At index -890830848: prob: 6.235778e-43, count: 10
39, -890830848, At index 4096: prob: 0.000000e+00, count: 140727914045119
40, 4096, At index 0: prob: 0.000000e+00, count: 105920833188
41, 0, At index 0: prob: 4.203895e-45, count: 140727915775920
42, 0, At index 5: prob: 0.000000e+00, count: 140727914280046
43, 5, At index -983893456: prob: 4.591354e-41, count: 140727914527280
44, -983893456, At index 1: prob: 0.000000e+00, count: 4096
45, 1, At index 0: prob: 0.000000e+00, count: 140727914188698
46, 0, At index -983893456: prob: 4.591354e-41, count: 140727914179194
47, -983893456, At index 131: prob: 0.000000e+00, count: 1914664585312
48, 131, At index 10: prob: 0.000000e+00, count: 140727914254959
49, 10, At index 72: prob: 0.000000e+00, count: 140727914527280
50, 72, At index -983893456: prob: 4.591354e-41, count: 10
51, -983893456, At index 0: prob: 0.000000e+00, count: 4294967295
52, 0, At index 24576: prob: 0.000000e+00, count: 140702208911160
53, 24576, At index -919683005: prob: 4.590514e-41, count: 140727914527280
54, -919683005, At index -919683010: prob: 4.590514e-41, count: 140727914045745
55, -919683010, At index 0: prob: 0.000000e+00, count: 140727914188698
56, 0, At index -983893360: prob: 3.082857e-44, count: 0
57, -983893360, At index 0: prob: 0.000000e+00, count: 0
58, 0, At index 55: prob: 0.000000e+00, count: 140727914254959
59, 55, At index 0: prob: 0.000000e+00, count: 0
60, 0, At index -983893456: prob: 4.591354e-41, count: 18446744069414608896
61, -983893456, At index -1: prob: nan, count: 140702208924636
62, -1, At index -1453387905: prob: 1.254162e-42, count: 4611686018427387904
63, -1453387905, At index -1453348608: prob: 3.363116e-44, count: 4611686018427387904
64, -1453348608, At index -983893456: prob: 4.591354e-41, count: 140702208902446
65, -983893456, At index -1453348656: prob: 3.363116e-44, count: 140727914527280
66, -1453348656, At index -919683010: prob: 4.590514e-41, count: 5
67, -919683010, At index 16: prob: 0.000000e+00, count: 140702208901562
68, 16, At index 24576: prob: 0.000000e+00, count: 140727913971049
69, 24576, At index -1453348616: prob: 3.363116e-44, count: 20
70, -1453348616, At index -1453348616: prob: 3.363116e-44, count: 0
71, -1453348616, At index -1453348616: prob: 3.363116e-44, count: 4611686018427387904
72, -1453348616, At index 0: prob: 0.000000e+00, count: 0
73, 0, At index 0: prob: 0.000000e+00, count: 0
74, 0, At index 0: prob: 0.000000e+00, count: 20
75, 0, At index 20: prob: 0.000000e+00, count: 16
76, 20, At index 0: prob: 0.000000e+00, count: 1296
77, 0, At index 0: prob: 1.875000e+00, count: 140702208892796
78, 0, At index -919683010: prob: 4.590514e-41, count: 1
79, -919683010, At index 1074790400: prob: 0.000000e+00, count: 0
80, 1074790400, At index -61569: prob: nan, count: 64

盡管所有這些值在 memset 中都是 0，即使在嵌套的 for 循環中設置了這些值之后也是如此。 有誰知道我做錯了什么？ 這些值應該寫入結構，但似乎它們不會持續存在，只是 go 在打印前回到 0。 代碼的 rest 不需要任何解釋，因為我認為我正在編寫的值的計算與錯誤無關。 該程序始終沒有錯誤地退出，所以我不確定為什么它不能正常工作。 謝謝！

Answer 1

您正在增加prob_count ，然后打印。 因此，您實際上並沒有打印剛剛設置的值，而是打印下一個尚未設置的成員的內容。 您在沒有 memset 的情況下看到的是不確定的值。 在 memset 之后，您會看到 0 值。

首先打印您更新的內容，然后增加。

Answer 2

問題在這里：

        prob_count++;
        printf("At index %d: prob: %e, count: %lu\n", prob_values[prob_count].index, prob_values[prob_count].probability, prob_values[prob_count].count);

您不會打印剛剛分配的結構，而只分配下一個歸零的結構。 它還會在最后一次迭代中導致未定義的行為。

它一定要是：

        printf("At index %d: prob: %e, count: %lu\n", prob_values[prob_count].index, prob_values[prob_count].probability, prob_values[prob_count].count);
        prob_count++;

此外：

(int) pow(n, 2)

處理整數時切勿使用浮點函數。 只需這樣做：

n * n

使用正確的尺寸類型。 Intead int使用size_t或ssize_t作為索引（如果索引可以為負）

Answer 3

似乎這是一個索引錯誤。 由於 prob_count++ 出現在 print 語句之前，我只是把它放在之后，問題似乎已經消失了，一切都按照它應該的方式打印了。 很奇怪，它沒有拋出錯誤，雖然！