Question

我想编辑文件的某些位。我打开文件并确定第一个字节指针。因此，在 ChangeBit 函数中，将一些位替换为1。当我想调试 ChangeBit 函数时，在for循环的第一次迭代中，调试光标从函数中跳出并且过程剂量不会终止，代码在函数后继续行。
怎么了？

void changeBit(char *ptr, int bitLen, int startPoint)
{
    ptr += startPoint / 8;
    startPoint %= 8;
    int tmpBit = 1;
    for (int i = startPoint; i < bitLen; i++)
    {
        ptr[i / 8] = (ptr[i / 8] | tmpBit << (7 - (i % 8)));
        //after this line in first iteration, debug cursor jump out of function
    }
}

int main(void)
{
// open and mmap() the file
    hFile = CreateFile(input_file_name, GENERIC_READ, 0, NULL, OPEN_EXISTING, 0, NULL);
    bytes_left = GetFileSize(hFile, NULL);
    hMap = CreateFileMapping(hFile, NULL, PAGE_READONLY, 0, 0, NULL);
    stream_pos = (unsigned char*)MapViewOfFile(hMap, FILE_MAP_READ, 0, 0, 0);   

    changeBit(stream_pos,5,0); // not working

    // copy all bytes to other memory but still not working
    char *OutFileContent;
    OutFileContent = malloc(bytes_left);
    memcpy(OutFileContent, stream_pos, bytes_left);

    changeBit(OutFileContent,5,0); // not working

    //write new bits stream to out file
}

指针有问题吗？

Answer 1

您可以在调试模式下使用“异常”设置窗口抛出异常：

https://msdn.microsoft.com/en-us/library/x85tt0dd.aspx

请同时检查以下代码：

hFile = CreateFile(input_file_name, GENERIC_READ, 0, NULL, OPEN_EXISTING, 0, NULL);
bytes_left = GetFileSize(hFile, NULL);
hMap = CreateFileMapping(hFile, NULL, PAGE_READONLY, 0, 0, NULL);
stream_pos = (unsigned char*)MapViewOfFile(hMap, FILE_MAP_READ, 0, 0, 0);

我像下面的示例一样更改它，它在我身边很有效：

HANDLE hFile = NULL;
HANDLE hMap = NULL;
char *stream_pos = NULL;
LPCTSTR input_file_name = _T("C:\\Users\\xxx\\Desktop\\Test\\test.txt");
DWORD bytes_left = 0;
hFile = CreateFile(input_file_name, GENERIC_ALL, 0, NULL, OPEN_EXISTING, 0, NULL);
bytes_left = GetFileSize(hFile, NULL);
hMap = CreateFileMapping(hFile, NULL, PAGE_READWRITE, 0, 0, NULL);
stream_pos = (char*)MapViewOfFile(hMap, FILE_MAP_ALL_ACCESS, 0, 0, 0);

该文件使用了只读属性，如果我们更改属性，它将运行良好。

在visual studio c中调试时跳出for循环中的函数

1 个答案: