我希望我的程序可以使用clang编译,且无警告。尽管编译后该函数似乎正常运行,但为什么会出现警告?我该如何处理这个警告?
$ clang cpu-disk-info.c
cpu-disk-info.c:108:17: warning: implicit declaration of function 'read' is
invalid in C99 [-Wimplicit-function-declaration]
while ((n = read(0, buf, betterSIZE)) > 0)
^
cpu-disk-info.c:109:5: warning: implicit declaration of function 'write' is
invalid in C99 [-Wimplicit-function-declaration]
write(1, buf, n);
^
代码
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define SIZE 1024
#define betterSIZE 4*SIZE /* read a better size at a time */
int main(int argc, char **argv)
{
/* copy(); */
/* make the names known */
void info(char file_name[]);
void buffered(char file_name[]);
void better_buffered(char file_name[]);
/* test */
clock_t toc;
clock_t tic = clock();
info("coreutils_8.13.orig.tar.gz");
info("coreutils_8.13.orig.tar.gz");
info("coreutils_8.13.orig.tar.gz");
info("coreutils_8.13.orig.tar.gz");
info("coreutils_8.13.orig.tar.gz");
toc = clock();
printf("Unbuffered: %f seconds\n", (double)(toc - tic) / CLOCKS_PER_SEC);
tic = clock();
buffered("coreutils_8.13.orig.tar.gz");
buffered("coreutils_8.13.orig.tar.gz");
buffered("coreutils_8.13.orig.tar.gz");
buffered("coreutils_8.13.orig.tar.gz");
buffered("coreutils_8.13.orig.tar.gz");
toc = clock();
printf("Buffered: %f seconds\n", (double)(toc - tic) / CLOCKS_PER_SEC);
tic = clock();
better_buffered("coreutils_8.13.orig.tar.gz");
better_buffered("coreutils_8.13.orig.tar.gz");
better_buffered("coreutils_8.13.orig.tar.gz");
better_buffered("coreutils_8.13.orig.tar.gz");
better_buffered("coreutils_8.13.orig.tar.gz");
toc = clock();
printf("Better buffered: %f seconds\n", (double)(toc - tic) / CLOCKS_PER_SEC);
return 0;
}
void info(char file_name[])
{
int ch;
FILE *fp;
fp = fopen(file_name,"r");
// read mode
if (fp == NULL)
{
perror(file_name);
exit(EXIT_FAILURE);
}
while ((ch = fgetc(fp)) != EOF)
{
//putchar(ch);
}
fclose(fp);
}
void buffered(char file_name[])
{
char buf[SIZE];
FILE *fp;
size_t nread;
fp = fopen(file_name, "r");
if (fp) {
while ((nread = fread(buf, 1, sizeof buf, fp)) > 0)
{
//fwrite(buf, 1, nread, stdout);
}
if (ferror(fp)) {
/* to do: deal with error */
}
fclose(fp);
}
}
void better_buffered(char file_name[])
{
char buf[betterSIZE];
FILE *fp;
size_t nread;
fp = fopen(file_name, "r");
if (fp) {
while ((nread = fread(buf, 1, sizeof buf, fp)) > 0)
{
//fwrite(buf, 1, nread, stdout);
}
if (ferror(fp)) {
/* to do: deal with error */
}
fclose(fp);
}
}
int copy() /* input2output ie anything to anything */
{
char buf[betterSIZE];
int n;
while ((n = read(0, buf, betterSIZE)) > 0)
write(1, buf, n);
return 0;
}
我正在使用Ubuntu(也希望代码能够在Solaris和BSD上运行)。
测试
$ ./benchm
Unbuffered: 0.670000 seconds
Buffered: 0.040000 seconds
Better buffered: 0.020000 seconds