在 c 中读取和写入文件 - 压缩矩阵

Question

I'm trying to write a compressed bits matrix to a and the read it back. The writing works great but the reading keeps failing and I dont understand why.

    typedef unsigned char BYTE;

    int saveCompressImageToFile(const char *fileName, const int *image, int row, int col)
    {
        FILE *fp = fopen(fileName, "wb");
        if (!fp)
            return 0;
        if (fwrite(&row, sizeof(int), 1, fp) != 1) {
            fclose(fp);
            return 0;
        }
        if (fwrite(&col, sizeof(int), 1, fp) != 1) {
            fclose(fp);
            return 0;
        }
        int byteCount = row * col / 8;
        if (byteCount * 8 < row * col)
            byteCount++;
        BYTE *data = (BYTE *)calloc(sizeof(BYTE), byteCount);
        int dataPos;
        int dataShift;
        for (int i = 0; i < row; i++) {
            for (int j = 0; j < col; j++) {
                dataPos = (i * col + j) / 8;
                dataShift =7 - (i * col + j) % 8;
                data[dataPos] |= (*(image + i * col + j)) << dataShift;
            }
        }
        if (fwrite(data, sizeof(BYTE), byteCount, fp) != byteCount) {
            fclose(fp);
            return 0;
        }
        return 1;
    }
    
    int * getImage_compress(const char * fileName, int * pRow, int * pCol)
{
    FILE* fp = fopen(fileName, "rb");
    if (!fp)
        return NULL;
    if (fread(pRow, sizeof(int), 1, fp) != 1)
    {
        fclose(fp);
        return NULL;
    }
    if (fread(pCol, sizeof(int), 1, fp) != 1)
    {
        fclose(fp);
        return NULL;
    }
    size_t mat_size = *pRow * (*pCol);
    int byteCount = mat_size / 8;
    if (byteCount * 8 < mat_size)
        byteCount++;
    BYTE* data = (BYTE*)malloc(sizeof(BYTE)*byteCount);
    if (!data)
    {
        fclose(fp);
        return NULL;
    }
    if (fread(data, sizeof(BYTE), byteCount, fp) != byteCount)
    {
        free(data);
        fclose(fp);
        return NULL;
    }
    fclose(fp);

    int* mat = (int*)calloc(mat_size, sizeof(int));
    if (!mat)
    {
        free(data);
        fclose(fp);
        return NULL;
    }
    for (int i = 0; i < mat_size; i++)
    {
        for (int j = 0; j < 8; j++)
        {
            mat[i * 8 + j] = (data[i] >> (7 - j)) & 0x1;
        }
    }
    free(data);
    return mat;
}

for some reason the function throws exception in the last line (return mat;) , "Starter.exe has triggered a breakpoint". occurred , what's going on over there? I've tried to debug that code and I can't tell why I can't return this value but I can access the cells in the debugger. any Suggestions?

Answer 1

Putting the comments in an answer:

So much wrong.

1. You need to fclose(fp) when there isn't an error in error in your first function. Otherwise not all of the data will be written. Or maybe nothing will be written.
2. fread(&data, ... would try to read the data over the pointer to the allocated space! It should just be fread(data, ...
3. You are reassembling the bits backwards from how you put them in. Change the reassembly to data[i] >> (7 - j) . Or assemble them in the other direction.
4. sizeof(BYTE) is 1. You mean 8. Use 8 for those.
5. Your allocation of mat when decompressing can be up to seven int s shorter than what you're writing. Either allocate mat large enough, using byteCount * 8 , or only decompress rows * columns int s.