无法读取文件？ [英] can't read file?
问题描述
以下代码用于读取名为input.txt的文件
#include< stdio.h>
int main（int argc，char * argv []）{
FILE * fp;
int ch;
fp = fopen（" input.txt"，" r"）;
ch = fscanf（fp，"％d"，& ch）;
printf（"％d \ n"，ch） ;
fclose（fp）;
返回0;
}
包含在input.txt中
3
3 14
2 8
-1 0
当我运行程序时输出为：
1
发生了什么？
为什么输出不是3？
尼克
nick< i1 *** *****@yahoo.com>写道：以下代码用于读取名为input.txt的文件
#include< stdio.h>
int main（int argc，char * argv []）{
FILE * fp;
int ch;
fp = fopen（" input.txt"，" r"）;
ch = fscanf（fp ，％d，& ch）;
printf（"％d \ n"，ch）;
fclose（fp）;
返回0;
}
包含在input.txt中
3
3 14
2 8
-1 0
当我运行程序时输出结果是：
1
是怎么回事？
为什么输出不是3？
fscanf（）返回扫描的项目数，在这种情况下，如果成功，则
为1。你正在传递& ch作为fcanf的参数（）
*和*你将结果赋给ch。不要那样做。
（我不确定它是否会调用未定义的行为，但它确实不是你想要的b $ b要做的事。）
-
Keith Thompson（The_Other_Keith） ks * **@mib.org < http://www.ghoti.net/~kst>
圣地亚哥超级计算机中心< *> < http://users.sdsc.edu/~kst>
我们必须做点什么。这是事情。因此，我们必须这样做。
ch = fscanf（fp，"％d"，& ch）;
此行是答案！因为fscanf（）返回一个int数字1，你的ch
得到它。
真正的方式是这样的
fscanf（fp，& ;％d"，& ch）;
写这样就好了，fscanf设置值为ch，你会发现
结果是3
祝你好运
usr_root
谢谢！
the following code is used to read a file called "input.txt"
# include <stdio.h>
int main(int argc,char *argv[]){
FILE *fp;
int ch;
fp=fopen("input.txt","r");
ch=fscanf(fp,"%d",&ch);
printf("%d\n",ch);
fclose(fp);
return 0;
}
the contains in "input.txt"
3
3 14
2 8
-1 0
when i run the program the output is:
1
what''s going on?
why the output is not 3?
Nick
nick <i1********@yahoo.com> writes:the following code is used to read a file called "input.txt"
# include <stdio.h>
int main(int argc,char *argv[]){
FILE *fp;
int ch;
fp=fopen("input.txt","r");
ch=fscanf(fp,"%d",&ch);
printf("%d\n",ch);
fclose(fp);
return 0;
}
the contains in "input.txt"
3
3 14
2 8
-1 0
when i run the program the output is:
1
what''s going on?
why the output is not 3?
fscanf() returns the number of items scanned, which in this case will
be 1 if it succeeds. You''re passing &ch as an argument to fcanf()
*and* you''re assigning the result to ch. Don''t do that.
(I''m not certain whether it invokes undefined behavior, but it''s
certainly not what you want to do .)
--
Keith Thompson (The_Other_Keith) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.
ch=fscanf(fp,"%d",&ch);
this line is the answer! because fscanf() return a int number 1,your ch
got it.
the true way was like this
fscanf(fp,"%d",&ch);
write like this is all ok,fscanf set value to ch,and you will found
the result is 3
best wishes
usr_root
thanks!
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