为什么我的这个程序没有将 fread 后的字符串输出来？
我的这个程序应该有字符串输出才是，但是运行的结果是16 bytes at byte 10: (null)/nPress any key to continue
出现了null的结果，但我的原文件123里面是有很长的内容的。
#include "stdafx.h"
#include <string.h>
#include <stdio.h>
int main( void )
{
FILE *fp;
fpos_t pos;
char buffer[50];
fp = fopen("f:\\123.txt", "r+");
if(fp == NULL)
{
printf("Trouble opening file/n");
}
else
{
pos = 10;
if( fsetpos( fp, &pos ) != 0 )
{
perror( "fsetpos error" );
}
else
{
fread( buffer, sizeof( char ), 16, fp );
printf( "16 bytes at byte %d: %.16s/n", pos, buffer );
}
}
fclose( fp );
return 0;
}
#include <string.h>
#include <stdio.h>
int main( void )
{
FILE *fp;
char buffer[50];
fp = fopen("123.txt", "r+");
if(fp == NULL)
{
printf("Trouble opening file/n");
}
else
{
fseek( fp, 10L, SEEK_SET );
fread( buffer, sizeof( char ), 16, fp );
printf( "16 bytes at byte %d: %.16s/n", 10, buffer );
}
fclose( fp );
return 0;
}
小心驶得万年船。
请检查每个函数的返回值！
参考下面：
#include <sys\stat.h>
#include <io.h>
#include <fcntl.h>
#include <share.h>
#include <stdlib.h>
#include <stdio.h>
#include <conio.h>
#include <string.h>
#define MAX_CLU_BYTES 65536
FILE *fo;
int fh;
__int64 offs,offs1;
__int64 rvi64;
int rv,wrv;
unsigned char buf[MAX_CLU_BYTES];
char ofn[_MAX_PATH];
char offstr[80];
void strcpybutcomma(char *t,char *s) {
char c;
while (1) {
c = *s++;
if (','!=c) *t++ = c;
if (0==c) break;
}
}
void main(int argc,char **argv) {
if (argc<3) {
printf("Copy File Tail.\n");
printf("Usage:\n");
printf(" cft filename.ext offset_begin[-offset_end]\n");
printf("Copy filename.ext offset_begin[-offset_end] to offset_begin[-offset_end]-filename.ext\n");
printf("Note: Byte at offset_end is NOT included.\n");
printf("Example:\n");
printf(" cft abc.rar 12345\n");
printf("Copy abc.rar offset 12345-end to 12345-abc.rar\n");
printf(" cft abc.rar 123-12345\n");
printf("Copy abc.rar offset 123-12345 to 123-12345-abc.rar\n");
printf(" cft abc.rar 0xAB-0xCD\n");
printf("Copy abc.rar offset 0xAB-0xCD to 0xAB-0xCD-abc.rar\n");
return;
}
strcpybutcomma(offstr,argv[2]);
rv=sscanf(offstr,"%I64i-%I64i",&offs,&offs1);
if (rv==0) {
printf("offset %s is not number\n",argv[2]);
return;
}
fh=_sopen(argv[1],_O_BINARY
[解决办法]
_O_RDONLY
[解决办法]
_O_RANDOM,_SH_DENYWR);
if (fh==-1) {
printf("_sopen %s errno=%d\n",argv[1],errno);
return;
}
if (rv==1) {
offs1=_filelengthi64(fh);
if (offs1==-1i64) {
printf("%I64=_filelengthi64 errno=%d\n",offs1,errno);
_close(fh);
return;
}
} else {//rv==2
if (offs1<offs) {
printf("%s offset_begin>offset_end error\n",argv[2]);
_close(fh);
return;
}
}
rvi64=_lseeki64(fh,offs,SEEK_SET);
if (rvi64!=offs) {
printf("%I64u=_lseeki64 %I64u errno=%d\n",rvi64,offs,errno);
_close(fh);
return;
}
sprintf(ofn,"%s-",offstr);
strcat(ofn,argv[1]);
fo=fopen(ofn,"wb");
if (fo==NULL) {
_close(fh);
printf("fopen %s error\n",ofn);
return;
}
cprintf("\n%I64u\r",offs);
while (1) {
rv=_read(fh,buf,(unsigned int)__min(offs1-offs,MAX_CLU_BYTES));
if (rv==0) break;//
if (rv<0) {
fclose(fo);
_close(fh);
printf("_read %s offset %I64u error\n",argv[1],offs);
return;
}
wrv=fwrite(buf,1,rv,fo);
if (wrv!=rv) {
fclose(fo);
_close(fh);
printf("fwrite %s error\n",ofn);
return;
} else {
offs+=rv;
cprintf("%I64u\r",offs);
if (offs>=offs1) break;//
}
}
fclose(fo);
_close(fh);
printf("Copy %s offset %s to %s OK.\n",argv[1],argv[2],ofn);
}
弄混了
