why open returns zero?

在试验open代码的时候，也犯了和这个哥们一样的错误。

如此低级的错误一定不要再犯了。

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Your conditional is off. Mind the parentheses. It should be:

if ((fd2 = open(logFile, O_RDWR |O_APPEND | O_CREAT , 0666)) == -1)
//                                                        ^^^    ^^^

Sometimes it might be best not to outsmart yourself:

int fd = open(...);

if (fd == -1) { DieWithError(); }