c程序编译警告：分配使指针从整数开始而没有强制转换[默认启用]

Question

when I compiling the a program named Online_ana.c (by running a makefile) with following line:

if ((fifoFile = open((FIFO1!=NULL) ? FIFO1 : "fifo1", O_RDONLY)) == -1)

encountered with such warnings:

Online_ana.c:54:17: warning: assignment makes pointer from integer without a cast [enabled by default]

whats is wrong with that? Hope that someone can help me. Thanks in advance!!

Answer 1

There's a couple things wrong with this.

1)You're assigning an integer value to a pointer. This isn't always wrong, but it is suspicious. It usually means a bug, but there are some situations where its ok. THat's why the compiler spits out a warning rather than an error. You should assure that you mean it.

2)Like @Barmar said, open returns an integer (a file handle) not a FILE*. If you're assigning one to the other its wrong.

3)Slightly unrelated, but assigning and comparing in an if like that is almost always a bad idea. Its too easy to accidentally type = somewhere you meant == and cause bugs. It should be avoided, use 1 line for assignment and 1 for comparison. I know old school C style is to use a single line, but these days its considered a bad idea.