C语言 如何使用 FILE 作为 C 中函数的参数？
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How do I use a FILE as a parameter for a function in C?
提问by Giga Tocka
I am learning C and I come from a Java background. I would appreciate it if I could have some guidance. Here is my code:
我正在学习 C，我来自 Java 背景。如果我能得到一些指导，我将不胜感激。这是我的代码：
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <unistd.h>
int main(void)
{
char *str = "test text\n";
FILE *fp;
fp = fopen("test.txt", "a");
write(fp, str);
}
void write(FILE *fp, char *str)
{
fprintf(fp, "%s", str);
}
When I try to compile, I get this error:
当我尝试编译时，出现此错误：
xxxx.c: In function ‘main':
xxxx.c:18: warning: passing argument 1 of ‘write' makes integer from pointer without a cast
/usr/include/unistd.h:363: note: expected ‘int' but argument is of type ‘struct FILE *'
xxxx.c:18: error: too few arguments to function ‘write'
xxxx.c: At top level:
xxxx.c:21: error: conflicting types for ‘write'
/usr/include/unistd.h:363: note: previous declaration of ‘write' was here
Any thoughts? Thanks for your time.
有什么想法吗？谢谢你的时间。
回答by squiguy
You are lacking a function prototype for your function. Also, writeis declared in unistd.hso that is why you get the first error. Try renaming that to my_writeor something. You really only need the stdio.hlibrary too as a side note, unless you plan on using other functions later. I added error checking for fopenas well as return 0;which should conclude every main function in C.
您的函数缺少函数原型。此外，write声明为 inunistd.h所以这就是为什么你会得到第一个错误。尝试将其重命名为my_write或其他名称。您实际上也只需要该stdio.h库作为旁注，除非您打算稍后使用其他功能。我添加了错误检查fopen以及return 0;哪个应该结束 C 中的每个主要函数。
Here is what I would do:
这是我会做的：
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <unistd.h>
void my_write(FILE *fp, char *str)
{
fprintf(fp, "%s", str);
}
int main(void)
{
char *str = "test text\n";
FILE *fp;
fp = fopen("test.txt", "a");
if (fp == NULL)
{
printf("Couldn't open file\n");
return 1;
}
my_write(fp, str);
fclose(fp);
return 0;
}
回答by Deepankar Bajpeyi
See man 2 writeon linux.
man 2 write在 linux 上查看。
#include <unistd.h>
ssize_t write(int fd, const void *buf, size_t count);
That is the prototype. You need to pass an integer file descriptor and not a file pointer.
If you want your own function Change the name to foo_writeor something
那就是原型。您需要传递整数文件描述符而不是文件指针。如果你想要自己的函数 把名字foo_write改成什么的
回答by Xymostech
There's already a system function called write. Just name your function something else, put a function declaration before you use it, and you'll be fine.
已经有一个名为write. 只需将您的函数命名为其他名称，在使用之前放置一个函数声明，就可以了。
