c - 尝试从文件中读取时无限循环

Question

我想从文件中读取字节然后重写它们。我确实喜欢这样:

FILE *fp;
int cCurrent;
long currentPos;

/* check if the file is openable */
if( (fp = fopen(szFileName, "r+")) != NULL )
{
    /* loop for each byte in the file crypt and rewrite */
    while(cCurrent != EOF)
    {
        /* save current position */
        currentPos = ftell(fp);
        /* get the current byte */
        cCurrent = fgetc(fp);
        /* XOR it */
        cCurrent ^= 0x10;
        /* take the position indicator back to the last position */
        fseek(fp, currentPos, SEEK_SET);
        /* set the current byte */
        fputc(cCurrent, fp);
    }

在文件上执行代码后，文件的大小在无限循环中增加。

我的代码有什么问题？

Answer 1

您正在用 0x10 XOR-ing cCurrent，即使它等于 EOF。一旦你XOR，它就不再是EOF，所以你的循环永远不会终止。

无限循环，看到EOF就从中间退出，像这样:

for (;;)  {
    /* save current position */
    currentPos = ftell(fp);
    /* get the current byte */
    if ((cCurrent = fgetc(fp)) == EOF) {
        break;
    }
    /* XOR it */
    cCurrent ^= 0x10;
    /* take the position indicator back to the last position */
    fseek(fp, currentPos, SEEK_SET);
    /* set the current byte */
    fputc(cCurrent, fp);
    /* reset stream for next read operation */
    fseek(fp, 0L, SEEK_CUR);
}