在项目 2017.1.exe 中的 0x0FDD053F (ucrtbased.dll) 处引发 bmp 文件异常错误：0xC0000005：访问冲突写入位置 0xCDCDCDCD

Question

在这段代码中，我尝试从每个像素的 RGB 值相同（如 ff ff ff）的 bmp 文件中获取每个像素中的第一个字节，并将这些值放入矩阵中以进行进一步操作。当调试器到达“从每个像素获取第一个字节”时，调试过程终止 并出现“在项目 2017.1.exe 中的 0x0FDD053F (ucrtbased.dll) 处引发异常：0xC0000005：访问冲突写入位置 0xCDCDCDCD”。有什么问题？（这是我第一次使用 bmp）感谢您的帮助！

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

main() {
    int width, height, w_count, h_count, padding;
    int **pix_mat;
    int a;
    FILE * dust_pic;
    fopen_s(&dust_pic, "d2.bmp", "rb");
    if (!dust_pic)
        printf_s("not found");
    fseek(dust_pic, 18, SEEK_SET);
    fread(&width, sizeof(int), 1, dust_pic);// getting width
    fread(&height, sizeof(int), 1, dust_pic);// getting height
    // FIND PADDING
    a = width;
    if (a % 4 != 0)
        padding = 4 - (a % 4);
    else
    padding = 0;

    //making matrix for pixels
    pix_mat = (int**)malloc(sizeof(int*)*height);
    for (h_count = 0; h_count < height; h_count++)
        pix_mat[h_count] = (int*)malloc(sizeof(int)*width);

    fseek(dust_pic, 54, SEEK_SET);
    // getting the first byte from each pixel
    for (h_count = 0; h_count < height; h_count++)
    {
        for (w_count = 0; w_count < width; w_count++)
        {
            fread(pix_mat[w_count][h_count], sizeof(char), 1, dust_pic);
            fseek(dust_pic, 2, SEEK_CUR);
        }
        fseek(dust_pic, padding, SEEK_CUR);
    }
    fclose(dust_pic);
    // print the matrix.
    for (h_count = 0; h_count < height; h_count++)
    {
        for (w_count = 0; w_count < width; w_count++)
            printf_s("[%d],[%d]=%d  ", w_count, h_count, pix_mat[w_count][h_count]);
        printf("\n");
    }
    // free array
    for (h_count = 0; h_count < height; h_count++)
        free(pix_mat[h_count]);
    free(pix_mat);
}

Answer 1

以下建议的代码：

1. 干净编译
2. 正确检查错误
3. 在发生任何错误事件后退出之前正确清理
4. 从文件中正确读取正确大小的数据并将该数据保存到正确声明的数组中
5. 正确引用内存中像素矩阵的行和列
6. 不纠正关于像素宽度、文件中像素偏移等的假设。

现在是代码

#include <stdio.h>  // fopen(), fclose(), perror(), fseek(), SEEK_SET
#include <stdlib.h> // exit(), EXIT_FAILURE, malloc(), calloc(), free()

// prototypes
void cleanup( FILE *dust_pic, size_t height, char **pix_mat );


int main( void )
{
    size_t width, height, w_count, h_count;
    long padding;
    char **pix_mat;

    FILE * dust_pic;
    dust_pic = fopen("d2.bmp", "rb");
    if (!dust_pic)
    {
        perror( "fopen failed" );
        exit( EXIT_FAILURE );
    }

    // implied else, fopen_s successful

    fseek(dust_pic, 18, SEEK_SET);
    // check for error

    if( 1 != fread(&width, sizeof(int), 1, dust_pic) )// getting width
    {
        perror( "fread for width of image, in pixels, failed" );
        fclose( dust_pic );
        exit( EXIT_FAILURE );
    }

    // implied else, fread successful

    if( 1 != fread(&height, sizeof(int), 1, dust_pic) )// getting height
    {
        perror( "fread for height of image, in pixels, failed" );
        fclose( dust_pic );
        exit( EXIT_FAILURE );
    }

    // implied else, fread successful

    // calculate PADDING
    if ( width % 4 != 0)
        padding = (long)(4 - (width % 4));
    else
        padding = 0;

    //making matrix for pixels
    pix_mat = calloc(height, sizeof(char*));
    // check for malloc status
    if( !pix_mat )
    {
        perror( "calloc for array of pointers to char failed" );
        fclose( dust_pic );
        exit( EXIT_FAILURE );
    }

    // implied else, calloc successful

    for (h_count = 0; h_count < height; h_count++)
    {
        pix_mat[h_count] = malloc(sizeof(char)*width);
        // check for malloc status
        if( !pix_mat[h_count] )
        {
            perror( "malloc failed" );
            fclose( dust_pic );
            exit( EXIT_FAILURE );
        }

        // implied else, malloc successful
    }

    // jump to beginning of pixel data in file
    if( -1 == fseek(dust_pic, 54, SEEK_SET) )
    {
        perror( "fseek to start of pixel data failed" );
        cleanup( dust_pic, height, pix_mat );
        exit( EXIT_FAILURE );
    }

    // implied else, fseek successful

    // get the first byte (red) from each pixel
    for (h_count = 0; h_count < height; h_count++)
    {
        for (w_count = 0; w_count < width; w_count++)
        {
            if( 1 != fread( &((pix_mat[h_count])[w_count]), sizeof(char), 1, dust_pic) )
            {
                perror( "fread of 'red' pixel value failed" );
                cleanup( dust_pic, height, pix_mat );
                exit( EXIT_FAILURE );
            }

            // implied else, fread successful

            if( -1 == fseek(dust_pic, 2, SEEK_CUR) )
            {
                perror( "fseek to skip green/blue pixels failed" );
                cleanup( dust_pic, height, pix_mat );
                exit( EXIT_FAILURE );
            }

            // implied else, fseek successful
        }

        if( -1 == fseek(dust_pic, padding, SEEK_CUR) )
        {
            perror( "fseek to skip padding failed" );
            cleanup( dust_pic, height, pix_mat );
            exit( EXIT_FAILURE );
        }

        // implied else, fseek successful
    }


    // print the matrix.
    for (h_count = 0; h_count < height; h_count++)
    {
        for (w_count = 0; w_count < width; w_count++)
            printf("[%lu],[%lu]=%3.3d  ", h_count, w_count, (pix_mat[h_count])[w_count]);
        printf("\n");
    }

    cleanup( dust_pic, height, pix_mat );
} // end function: main


void cleanup( FILE *dust_pic, size_t height, char **pix_mat )
{
    // free array
    for (size_t h_count = 0; h_count < height; h_count++)
        free(pix_mat[h_count]);
    free(pix_mat);

    fclose( dust_pic );
} // end function: cleanup