導致分段錯誤的GMP mpf函數

Question

我找不出導致此錯誤的原因。我剛剛在Ubuntu上安裝了GMP。這是AMD cpu上的64位操作系統（不確定是否重要）。我不斷收到分段錯誤。

#include <stdio.h> 
#include <stdlib.h> 
#include <gmp.h> 
#include <time.h> 


int main(int argc, char** argv) 
{ 
    mpz_t sum, fac; 
    mpf_t fsum, ffac; 
    int i; 
    time_t t; 

    mpz_init_set_ui(sum, 1); 
    mpz_init_set_ui(fac, 1); 

    t = time(NULL); 

    for(i = 10000; i >= 1; --i) 
    { 
    mpz_mul_ui(fac, fac, i); 
    mpz_add(sum, sum, fac); 
    if(i % 10000 == 0) 
    { 
     printf("%d\n", i); 
    } 
    } 

    printf("Time %d\n", (time(0) - t)); 

    mpf_init(fsum); 
    mpf_init(ffac); 
    mpf_set_z(fsum, sum); 
    mpf_set_z(ffac, fac); 


    mpz_clear(sum); 
    mpz_clear(fac); 

    mpf_div(fac, sum, fac); 

    mpf_out_str(stdout, 10, 50, fac); 

    mpf_clear(fsum); 
    mpf_clear(ffac); 
    return(EXIT_SUCCESS); 
} 

此代碼輸出以下...

10000 
Time 0 
Segmentation fault (core dumped) 

我然後試圖運行此程序以Valgrind的，這是輸出。

==25427== Memcheck, a memory error detector 
==25427== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al. 
==25427== Using Valgrind-3.10.0.SVN and LibVEX; rerun with -h for copyright info 
==25427== Command: /home/chase/NetBeansProjects/GmpECalc/dist/Debug/GNU-Linux-x86/gmpecalc 
==25427== 
10000 
Time 1 
==25427== Invalid read of size 8 
==25427== at 0x4E8E590: __gmpn_copyi (in /usr/lib/x86_64-linux-gnu/libgmp.so.10.1.3) 
==25427== by 0x400B27: main (main.c:40) 
==25427== Address 0x73b0000073c is not stack'd, malloc'd or (recently) free'd 
==25427== 
==25427== 
==25427== Process terminating with default action of signal 11 (SIGSEGV) 
==25427== Access not within mapped region at address 0x73B0000073C 
==25427== at 0x4E8E590: __gmpn_copyi (in /usr/lib/x86_64-linux-gnu/libgmp.so.10.1.3) 
==25427== by 0x400B27: main (main.c:40) 
==25427== If you believe this happened as a result of a stack 
==25427== overflow in your program's main thread (unlikely but 
==25427== possible), you can try to increase the size of the 
==25427== main thread stack using the --main-stacksize= flag. 
==25427== The main thread stack size used in this run was 8388608. 
==25427== 
==25427== HEAP SUMMARY: 
==25427==  in use at exit: 48 bytes in 2 blocks 
==25427== total heap usage: 3,706 allocs, 3,704 frees, 27,454,096 bytes allocated 
==25427== 
==25427== LEAK SUMMARY: 
==25427== definitely lost: 0 bytes in 0 blocks 
==25427== indirectly lost: 0 bytes in 0 blocks 
==25427==  possibly lost: 0 bytes in 0 blocks 
==25427== still reachable: 48 bytes in 2 blocks 
==25427==   suppressed: 0 bytes in 0 blocks 
==25427== Rerun with --leak-check=full to see details of leaked memory 
==25427== 
==25427== For counts of detected and suppressed errors, rerun with: -v 
==25427== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0) 
Segmentation fault (core dumped) 

該錯誤似乎發生在mpf_div函數。但是，如果我刪除了這個函數，錯誤將發生在mpf_out_str處。我也嘗試初始化ffac和fsum來加倍（而不是將它們設置爲fac和sum），並且我得到相同的錯誤。

Answer 1

問題是在這行：

mpz_clear(sum); // You clear the variables, GMP deallocates their memory 
mpz_clear(fac); 

mpf_div(fac, sum, fac); // You use cleared variables, segfault 

也許你的意思是：

mpf_div(ffac, fsum, ffac);