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[英]implicit declaration of function 'link'; did you mean 'unlink'?,implicit declaration of function 'symlink'
[英]implicit declaration of function ‘write’; did you mean ‘fwrite’?
我编译了一个简单的笔记程序示例,该程序使用书中的文件描述符,并且我收到了一些与“写入”和“关闭”函数以及使用“strncat”相关的编译器错误功能。 这是代码:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <sys/stat.h>
void usage(char *prog_name, char *filename) {
printf("Usage: %s <data to add to %s>\n", prog_name, filename);
exit(0);
}
void fatal(char *); // A function for fatar errors
void *ec_malloc(unsigned int); // An error-checked malloc() wrapper
int main(int argc, char *argv[]) {
int fd; // file descriptor
char *buffer, *datafile;
buffer = (char *) ec_malloc(100);
datafile = (char *) ec_malloc(20);
strcpy(datafile, "/tmp/notes");
if (argc < 2) // If there aren't command-line arguments,
usage(argv[0], datafile); // display usage message and exit.
strcpy(buffer, argv[1]); // Copy into buffer.
printf("[DEBUG] buffer @ %p: \'%s\'\n", buffer, buffer);
printf("[DEBUG] datafile @ %p: \'%s\'\n", datafile, datafile);
strncat(buffer, "\n", 1); // Add a newline on the end.
// Opening file
fd = open(datafile, O_WRONLY|O_CREAT|O_APPEND, S_IRUSR|S_IWUSR);
if(fd == -1)
fatal("in main() while opening file");
printf("[DEBUG] file descriptor is %d\n", fd);
//Writing data
if(write(fd, buffer, strlen(buffer)) == -1)
fatal ("in main() while writing buffer to file");
//Closing file
if(close(fd) == -1)
fatal ("in main() while closing file");
printf("Note has been saved.\n");
free(buffer);
free(datafile);
}
// A function to display and error message and then exit
void fatal(char *message) {
char error_message[100];
strcpy(error_message, "[!!] Fatal Error ");
strncat(error_message, message, 83);
perror(error_message);
exit(-1);
}
// An error-checked malloc() wrapper function
void *ec_malloc(unsigned int size) {
void *ptr;
ptr = malloc(size);
if(ptr == NULL);
fatal("in ec_malloc() on memory allocation");
return ptr;
}
这是编译器错误:
implenote.c: In function ‘main’:
simplenote.c:39:5: warning: implicit declaration of function ‘write’; did you mean ‘fwrite’? [-Wimplicit-function-declaration]
39 | if(write(fd, buffer, strlen(buffer)) == -1)
| ^~~~~
| fwrite
simplenote.c:42:5: warning: implicit declaration of function ‘close’; did you mean ‘pclose’? [-Wimplicit-function-declaration]
42 | if(close(fd) == -1)
| ^~~~~
| pclose
simplenote.c:31:2: warning: ‘strncat’ specified bound 1 equals source length [-Wstringop-overflow=]
31 | strncat(buffer, "\n", 1); // Add a newline on the end.
代码是从书中复制的,没有做任何改动,我想知道为什么会发生这种情况以及我可以做些什么来使代码运行。 请注意,这本书(黑客:剥削的艺术,第二版)有点过时,于 2008 年发行。
要访问 Posix 低级文件接口,例如open
、 read
、 write
和close
,您应该包含<unistd.h>
。
但是请注意,您的程序似乎不需要如此低级的接口,您可以考虑使用在<stdio.h>
声明的标准流创建输出文件,使用fopen
、 fputs
或fprintf
和fclose
。
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