c - GCC 中的动态分配指针数组不匹配

Question

Minimally Verifiable Source Code - I think.我正在尝试在函数中使用指针数组的动态分配来创建双双指针数组。当我在结构引用之外使用代码时，它会起作用。当我尝试通过指针引用它时，它没有。我究竟做错了什么？

此代码适用于 GCC 4.9.2

gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/4.9/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 4.9.2-10ubuntu13' --with-bugurl=file:///usr/share/doc/gcc-4.9/README.Bugs --enable-languages=c,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-4.9 --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.9 --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-gnu-unique-object --disable-vtable-verify --enable-plugin --with-system-zlib --disable-browser-plugin --enable-java-awt=gtk --enable-gtk-cairo --with-java-home=/usr/lib/jvm/java-1.5.0-gcj-4.9-amd64/jre --enable-java-home --with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-4.9-amd64 --with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-4.9-amd64 --with-arch-directory=amd64 --with-ecj-jar=/usr/share/java/eclipse-ecj.jar --enable-objc-gc --enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix

int main(int argc, char **argv) 
{
    double ** array;
    double row[6] = { 1.2,   2.3,   3.0,   4,   5,   6  };
    int i;
  int j;
    array = (double **) malloc( 50* sizeof(double *  )  );
    for ( i = 0; i <  50; i++)
    {
        array[i] = (double *) malloc( 6 * sizeof(double  )  );
    }
    for (j =0; j < 50; j++)
    for ( i = 0; i <  6; i++)
    {
        array[j][i] = row[i];
    }
    for (j =0; j < 50; j++)
    {   
        for (i = 0; i < 6; i++ )
        { 
            printf("%f ", ( array[0][i]) );
        }
        printf("\n ");
    }
  exit(0);  // Use exit() to exit a program, do not use 'return' from main()
}

但是这段代码没有:

double ** create_array( unsigned int length,  unsigned int row)
{
    double ** array;
    int i;

    array = (double **) malloc( length * sizeof(double *  )  );
    for ( i = 0; i <  length; i++)
    {
        array[i] = (double *) malloc( row * sizeof(double  )  );
    }
    return array;
} 

我把双指针数组放在一个结构中

typedef struct
{
        // the data area
    double ** array;
    // the number of rows in the entire entry
    unsigned int length;
    // the size of the double entity of array size
    unsigned int rowsize;
    // the current starting point 
    int start;
    // the current ending point
    int end;
    // the amount of the last write action
    // assumes the number of write in order
    unsigned int last_write[100];
    // the number of writes
    unsigned int write_count;
} DRingBuffer;

然后通过如下函数调用访问:

int DRingBuffer_printrow(DRingBuffer *buffer,  unsigned int row  )

当我调用该函数然后尝试访问它的成员时出现错误。

        printf("%f ", (buffer->array[3][2]));

这是很多代码，但有人要求它。

 DRingBuffer *DRingBuffer_create(unsigned int length,  unsigned int row  )
    {
        int i =0;
        DRingBuffer *buffer = malloc( sizeof(DRingBuffer) );
        buffer->length  = length;
        buffer->rowsize =  row;
        buffer->start = 0;
        buffer->end = 0;
        buffer->array   = create_array(  length,  row);
        if ( buffer->array  <= 0  )
        {
            printf("ERROR: allocating arrays");
            exit( -1);
        }
        return buffer;
    }

Answer 1

您在 create_array() 中的代码应该没问题。它对我有用。您没有在使用它的地方显示代码，因此我们无法确定您是如何滥用它的，但看起来您确实在滥用它。

这是对您的代码的改编:

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

static
double **create_array(unsigned int length,  unsigned int row)
{
    double **array;

    array = (double **) malloc(length * sizeof(double *));
    for (unsigned int i = 0; i <  length; i++)
    {
        array[i] = (double *) malloc(row * sizeof(double));
    }
    return array;
}

int main(void)
{
    double **array;
    double row[6] = { 1.2,   2.3,   3.0,   4,   5,   6  };

    array = (double **) malloc(50 * sizeof(double *));
    for (int i = 0; i <  50; i++)
    {
        array[i] = (double *) malloc(6 * sizeof(double));
    }

    for (int j = 0; j < 50; j++)
    {
        for (int i = 0; i <  6; i++)
        {
            array[j][i] = row[i] + (i + 1) * (j + 1);
        }
    }
    for (int j = 0; j < 50; j++)
    {
        for (int i = 0; i < 6; i++)
        {
            printf("%6.1f ", (array[j][i]));
        }
        putchar('\n');
    }

    for (int j = 0; j < 50; j++)
        free(array[j]);
    free(array);

    double **array2 = create_array(50, 6);

    for (int j = 0; j < 50; j++)
    {
        for (int i = 0; i <  6; i++)
        {
            array2[j][i] = row[i] + (i + 1) * (j + 1);
        }
    }
    for (int j = 0; j < 50; j++)
    {
        for (int i = 0; i < 6; i++)
        {
            printf("%6.1f ", (array2[j][i]));
        }
        putchar('\n');
    }

    for (int j = 0; j < 50; j++)
        free(array2[j]);
    free(array2);

    return(0);
}

在 Mac OS X 10.11.1 El Capitan 上测试，它产生:

   2.2    4.3    6.0    8.0   10.0   12.0 
   3.2    6.3    9.0   12.0   15.0   18.0 
   4.2    8.3   12.0   16.0   20.0   24.0 
   5.2   10.3   15.0   20.0   25.0   30.0 
   6.2   12.3   18.0   24.0   30.0   36.0 
   7.2   14.3   21.0   28.0   35.0   42.0 
   8.2   16.3   24.0   32.0   40.0   48.0 
   9.2   18.3   27.0   36.0   45.0   54.0 
  10.2   20.3   30.0   40.0   50.0   60.0 
  11.2   22.3   33.0   44.0   55.0   66.0 
  12.2   24.3   36.0   48.0   60.0   72.0 
  13.2   26.3   39.0   52.0   65.0   78.0 
  14.2   28.3   42.0   56.0   70.0   84.0 
  15.2   30.3   45.0   60.0   75.0   90.0 
  16.2   32.3   48.0   64.0   80.0   96.0 
  17.2   34.3   51.0   68.0   85.0  102.0 
  18.2   36.3   54.0   72.0   90.0  108.0 
  19.2   38.3   57.0   76.0   95.0  114.0 
  20.2   40.3   60.0   80.0  100.0  120.0 
  21.2   42.3   63.0   84.0  105.0  126.0 
  22.2   44.3   66.0   88.0  110.0  132.0 
  23.2   46.3   69.0   92.0  115.0  138.0 
  24.2   48.3   72.0   96.0  120.0  144.0 
  25.2   50.3   75.0  100.0  125.0  150.0 
  26.2   52.3   78.0  104.0  130.0  156.0 
  27.2   54.3   81.0  108.0  135.0  162.0 
  28.2   56.3   84.0  112.0  140.0  168.0 
  29.2   58.3   87.0  116.0  145.0  174.0 
  30.2   60.3   90.0  120.0  150.0  180.0 
  31.2   62.3   93.0  124.0  155.0  186.0 
  32.2   64.3   96.0  128.0  160.0  192.0 
  33.2   66.3   99.0  132.0  165.0  198.0 
  34.2   68.3  102.0  136.0  170.0  204.0 
  35.2   70.3  105.0  140.0  175.0  210.0 
  36.2   72.3  108.0  144.0  180.0  216.0 
  37.2   74.3  111.0  148.0  185.0  222.0 
  38.2   76.3  114.0  152.0  190.0  228.0 
  39.2   78.3  117.0  156.0  195.0  234.0 
  40.2   80.3  120.0  160.0  200.0  240.0 
  41.2   82.3  123.0  164.0  205.0  246.0 
  42.2   84.3  126.0  168.0  210.0  252.0 
  43.2   86.3  129.0  172.0  215.0  258.0 
  44.2   88.3  132.0  176.0  220.0  264.0 
  45.2   90.3  135.0  180.0  225.0  270.0 
  46.2   92.3  138.0  184.0  230.0  276.0 
  47.2   94.3  141.0  188.0  235.0  282.0 
  48.2   96.3  144.0  192.0  240.0  288.0 
  49.2   98.3  147.0  196.0  245.0  294.0 
  50.2  100.3  150.0  200.0  250.0  300.0 
  51.2  102.3  153.0  204.0  255.0  306.0 
   2.2    4.3    6.0    8.0   10.0   12.0 
   3.2    6.3    9.0   12.0   15.0   18.0 
   4.2    8.3   12.0   16.0   20.0   24.0 
   5.2   10.3   15.0   20.0   25.0   30.0 
   6.2   12.3   18.0   24.0   30.0   36.0 
   7.2   14.3   21.0   28.0   35.0   42.0 
   8.2   16.3   24.0   32.0   40.0   48.0 
   9.2   18.3   27.0   36.0   45.0   54.0 
  10.2   20.3   30.0   40.0   50.0   60.0 
  11.2   22.3   33.0   44.0   55.0   66.0 
  12.2   24.3   36.0   48.0   60.0   72.0 
  13.2   26.3   39.0   52.0   65.0   78.0 
  14.2   28.3   42.0   56.0   70.0   84.0 
  15.2   30.3   45.0   60.0   75.0   90.0 
  16.2   32.3   48.0   64.0   80.0   96.0 
  17.2   34.3   51.0   68.0   85.0  102.0 
  18.2   36.3   54.0   72.0   90.0  108.0 
  19.2   38.3   57.0   76.0   95.0  114.0 
  20.2   40.3   60.0   80.0  100.0  120.0 
  21.2   42.3   63.0   84.0  105.0  126.0 
  22.2   44.3   66.0   88.0  110.0  132.0 
  23.2   46.3   69.0   92.0  115.0  138.0 
  24.2   48.3   72.0   96.0  120.0  144.0 
  25.2   50.3   75.0  100.0  125.0  150.0 
  26.2   52.3   78.0  104.0  130.0  156.0 
  27.2   54.3   81.0  108.0  135.0  162.0 
  28.2   56.3   84.0  112.0  140.0  168.0 
  29.2   58.3   87.0  116.0  145.0  174.0 
  30.2   60.3   90.0  120.0  150.0  180.0 
  31.2   62.3   93.0  124.0  155.0  186.0 
  32.2   64.3   96.0  128.0  160.0  192.0 
  33.2   66.3   99.0  132.0  165.0  198.0 
  34.2   68.3  102.0  136.0  170.0  204.0 
  35.2   70.3  105.0  140.0  175.0  210.0 
  36.2   72.3  108.0  144.0  180.0  216.0 
  37.2   74.3  111.0  148.0  185.0  222.0 
  38.2   76.3  114.0  152.0  190.0  228.0 
  39.2   78.3  117.0  156.0  195.0  234.0 
  40.2   80.3  120.0  160.0  200.0  240.0 
  41.2   82.3  123.0  164.0  205.0  246.0 
  42.2   84.3  126.0  168.0  210.0  252.0 
  43.2   86.3  129.0  172.0  215.0  258.0 
  44.2   88.3  132.0  176.0  220.0  264.0 
  45.2   90.3  135.0  180.0  225.0  270.0 
  46.2   92.3  138.0  184.0  230.0  276.0 
  47.2   94.3  141.0  188.0  235.0  282.0 
  48.2   96.3  144.0  192.0  240.0  288.0 
  49.2   98.3  147.0  196.0  245.0  294.0 
  50.2  100.3  150.0  200.0  250.0  300.0 
  51.2  102.3  153.0  204.0  255.0  306.0 

在 valgrind 下运行时，它也不会泄漏任何内存或显示任何内存滥用.或者，至少，在 El Capitan 上，内存泄漏全部来自系统代码，完全不受像你我这样的凡人的控制。

有些人会责备您(可能还有我)强制转换 malloc() 的结果。了解他们的敏感度，谨慎行事。如果你像我一样使用严格的编译警告进行编译，你就不会遇到问题:

$ gcc -O3 -g -std=c11 -Wall -Wextra -Wmissing-prototypes -Wstrict-prototypes \
>     -Wold-style-definition -Werror ddda.c -o ddda
$