C++ GMP mpz_init（）導致分割錯誤11

Question

我有一個程序，收到Segmentation Fault 11通知main的簡單性。這裏是我的整個工作的腳本：

#include <iostream> 
#include "gmp.h" 

void 
makeprime() 
{ 
    // *********************** VARIABLE DECLARATION *********************** // 
    // initilize the variables as gmp class instances 
    mpz_t l, rand; 
    unsigned long seed; 
    // perform inits to create variable pointers with 0 value 
    mpz_inits(l, rand); 
    //mpz_init(rand); 

    // calculate the random number floor 
    mpz_ui_pow_ui(l, 2, 199); 

    // initilze the state object for the random generator functions 
    gmp_randstate_t rstate; 
    // initialize state for a Mersenne Twister algorithm. This algorithm is fast and has good randomness properties. 
    gmp_randinit_mt(rstate); 

    // create the generator seed for the random engine to reference 
    gmp_randseed_ui(rstate, seed); 

    /* 
    Function: 
    int mpz_probab_prime_p (const mpz_t n, int reps) 

    Determine whether n is prime. Return 2 if n is definitely prime, return 1 if n is probably prime (without being certain), 
    or return 0 if n is definitely composite. 
    */ 
    do { 
     // return a uniformly distributed random number in the range 0 to n-1, inclusive. 
     mpz_urandomb(rand, rstate, 310); 

     // add the random number to the low number, which will make sure the random number is between the low and high ranges 
     mpz_add(rand, rand, l); 

     gmp_printf("randomly generated number: %Zd\n", rand); 

    } while (!(mpz_probab_prime_p(rand, 25)));   

    // *********************** GARBAGE COLLECTION *********************** // 
    // empty the memory location for the random generator state 
    gmp_randclear(rstate); 
    // clear the memory locations for the variables used to avoid leaks 
    mpz_clear(l); 
    mpz_clear(rand); 
} 

int 
main (void) 
{ 
    makeprime(); 
    return 0; 
} 

好了，現在我會在開頭添加下面兩行主（不改變其他任何有關腳本）：

int 
main (void) 
{ 
    mpz_t r;  //added this line 
    mpz_init (r); //and added this line 

    makeprime(); 
    return 0; 
} 

現在我的計劃不正確執行，也不打印或執行makeprime()，而是我得到一個Segmentation Fault 11通知。

什麼給？我在這裏做錯了什麼？

Answer 1

我試圖用gdb來調試你的代碼，它給了我一個段錯誤mpz_inits(l, rand)。然後我修改了這一行，現在它不會給出段錯誤。我會看看我是否能找到段錯誤的原因。

#include <iostream> 
#include "gmp.h" 

void 
makeprime() 
{ 
    // *********************** VARIABLE DECLARATION *********************** // 
    // initilize the variables as gmp class instances 
    mpz_t l, rand; 
    unsigned long seed; 
    // perform inits to create variable pointers with 0 value 

    //mpz_inits(l, rand); 
    mpz_init(rand); 
    mpz_init(l); 

    // calculate the random number floor 
    mpz_ui_pow_ui(l, 2, 199); 

    // initilze the state object for the random generator functions 
    gmp_randstate_t rstate; 
    // initialize state for a Mersenne Twister algorithm. This algorithm is fast and has good randomness properties. 
    gmp_randinit_mt(rstate); 

    // create the generator seed for the random engine to reference 
    gmp_randseed_ui(rstate, seed); 

    /* 
    Function: 
    int mpz_probab_prime_p (const mpz_t n, int reps) 

    Determine whether n is prime. Return 2 if n is definitely prime, return 1 if n is probably prime (without being certain), 
    or return 0 if n is definitely composite. 
    */ 
    do { 
     // return a uniformly distributed random number in the range 0 to n-1, inclusive. 
     mpz_urandomb(rand, rstate, 310); 

     // add the random number to the low number, which will make sure the random number is between the low and high ranges 
     mpz_add(rand, rand, l); 

     gmp_printf("randomly generated number: %Zd\n", rand); 

    } while (!(mpz_probab_prime_p(rand, 25)));   

    // *********************** GARBAGE COLLECTION *********************** // 
    // empty the memory location for the random generator state 
    gmp_randclear(rstate); 
    // clear the memory locations for the variables used to avoid leaks 
    mpz_clear(l); 
    mpz_clear(rand); 
} 

int 
main (void) 
{ 
    makeprime(); 
    return 0; 
} 

編輯：

我看着GMP Documentation和它說以下有關mpz_inits。

- Function：無效mpz_init（mpz_t X）

初始化的x，並將其值設定爲0。

- Function：無效mpz_inits（mpz_t X，。 ...）

初始化一個空終止列表的mpz_t變量，並將其值設置爲0.

您必須以NULL結束要初始化的變量列表。所以你需要用mpz_inits(l, rand, NULL)代替mpz_inits(l, rand)，它工作得很好。

編輯：

你忘了初始化種子。在函數makeprime中，你聲明unsigned long seed;，但不要爲種子分配一個值，因此每次得到相同的數字，因爲種子的值對於每次執行都是相同的。

通常使用系統時間初始化隨機種子。您可以使用

seed = (int) time(NULL); 

在聲明後面初始化種子。一切工作正常然後（不要忘記包括ctime或time.h）。