非常奇怪的C异常 [英] VERY strange C anomaly
问题描述
请考虑以下摘录，附带相关的
声明。
首先，标有**，***，**的行**一开始不是
应该在开头有这些明星;他们只习惯直接关注
.
假设，首先，****的行不存在。
p_num以某种方式通过
sscanf命令（***）从之前的值变为0，甚至不涉及p_num。我不能理解它，我怎么可能做任何会修改其值的b / b
。标有**的行被添加以确定那是
确实是导致问题的行。 （之前的值为1，之后的值为0）。
然后我添加了标记为****的行以解决问题，但是是
这种廉价修复的理念非常糟糕的编程风格，
我想知道是否有人可以对此有所了解。
代码如下。
int main（int argc，char ** argv）{
int pktsize，interval，numgums，p_pktsize，p_interval，p_num;
char trial，p_trial;
int wtf;
char buffer [200];
FILE * fp;
fp = fopen（argv [1]， " r"）;
....
while（fgets（buffer，160，fp）！= NULL）{
** printf（" p_numgums怎么突然变为0 =％d？！？！\ n"，p_num）;
**** wtf = p_num;
*** if（sscanf（缓冲区，％d％d％d％1s％* d％lf，& pktsize，
& interval，& numgums ，& trial，& commrate）== 5）{
**** p_num = wtf;
** printf（ok，now what？％ d \ n"，p_num）;
printf（" from the string |％s"，buffer）;
printf（" cur data set：pktsize = ％d interval =％d num =％d trial =％c cmr =％f \ n"，
pktsize，interval，numgums，trial，commrate）;
printf（" prev data set：pktsize =％d interval =％d num = ％d trial =％c cmr =％f \ n"，
p_pktsize，p_interval，p_num，p_trial，p_commrate）;
if（count = = -1）{
count = 1; ++ j;
min = max = runtot = commrate;
}否则if（（p_pktsize == pktsize）&&（p_interval ==
interval）&&（p_num == numgums））{
++ count; ++ j;
runtot + = commrate;
if（fcompare（commrate，min）< 0）min = commrate;
if （fcompare（max，commrate）< 0）max = commrate;
} else {
printf（"％d \ t％d \ t％d） \t％c \％％d \ t％f \ t％f \ t％f \ n"，
p_pktsize，p_interval，p_num，p_trial，count，
runtot / count，max，min）;
count = 1; j = 1;
min = max = runtot = commrate;
}
p_pktsize = pktsize;
p_interval = interval;
printf（" numgums已从％d更改，p_num）;
p_num = numgums;
printf（"到％d \ n"，p_num）;
p_trial = trial;
p_commrate = commrate;
}
}
返回0;
}
我通过argv提供文件的头（-n10） [1]看起来像这样：
----
1000 10 1 a 10 91.041515 1500
1000 10 1 b 11 91.036757 1491
1000 10 1 c 12 87.535014 1500
1000 10 3 a 10 51.517332 859
1000 10 3 a 11 54.095827 910
1000 10 3 a 12 52.226982 890
1000 10 3 b 20 37.465007 629
1000 10 3 b 21 47.486709 786
1000 10 3 b 22 49.602106 829
1000 10 3 c 30 36.402570 629
----
非常困惑，
-Bernard Liang
Consider the following excerpt below, with the included relevant
declarations.
Firstly, the lines marked with **, ***, **** at the beginning are not
supposed to have those stars at the beginning; they are only used to
direct attention.
Suppose, first of all, that the lines with the **** are not present.
p_num is somehow getting changed from its previous value to 0 by the
sscanf command (***) that doesn''t even involve p_num. I cannot
understand it, how I could possibly be doing anything that would modify
its value. The lines marked ** were added to determine that that was
indeed the line causing the problem. (the value was 1 before, and 0 after).
I then added the lines marked **** to remedy the problem, but being of
the philosophy that such "cheap fixes" are very poor programming style,
I wanted to see if anyone could shed some insight on this.
Code follows.
int main(int argc, char** argv) {
int pktsize, interval, numgums, p_pktsize, p_interval, p_num;
char trial, p_trial;
int wtf;
char buffer[200];
FILE* fp;
fp = fopen(argv[1], "r");
....
while (fgets(buffer, 160, fp) != NULL) {
**printf("how did p_numgums suddenly change to 0=%d?!?!\n", p_num);
****wtf = p_num;
*** if (sscanf(buffer, "%d %d %d %1s %*d %lf", &pktsize,
&interval, &numgums, &trial, &commrate) == 5) {
****p_num = wtf;
**printf("ok, now what? %d\n", p_num);
printf("from the string |%s", buffer);
printf(" cur data set: pktsize=%d interval=%d num=%d trial=%c cmr=%f\n",
pktsize, interval, numgums, trial, commrate);
printf("prev data set: pktsize=%d interval=%d num=%d trial=%c cmr=%f\n",
p_pktsize, p_interval, p_num, p_trial, p_commrate);
if (count == -1) {
count = 1; ++j;
min = max = runtot = commrate;
} else if ((p_pktsize == pktsize) && (p_interval ==
interval) && (p_num == numgums)) {
++count; ++j;
runtot += commrate;
if (fcompare(commrate, min) < 0) min = commrate;
if (fcompare(max, commrate) < 0) max = commrate;
} else {
printf("%d\t%d\t%d\t%c\t%d\t%f\t%f\t%f\n",
p_pktsize, p_interval, p_num, p_trial, count,
runtot / count, max, min);
count = 1; j = 1;
min = max = runtot = commrate;
}
p_pktsize = pktsize;
p_interval = interval;
printf("numgums was changed from %d", p_num);
p_num = numgums;
printf("to %d\n", p_num);
p_trial = trial;
p_commrate = commrate;
}
}
return 0;
}
The head (-n10) of the file I am feeding it via argv[1] looks likes this:
----
1000 10 1 a 10 91.041515 1500
1000 10 1 b 11 91.036757 1491
1000 10 1 c 12 87.535014 1500
1000 10 3 a 10 51.517332 859
1000 10 3 a 11 54.095827 910
1000 10 3 a 12 52.226982 890
1000 10 3 b 20 37.465007 629
1000 10 3 b 21 47.486709 786
1000 10 3 b 22 49.602106 829
1000 10 3 c 30 36.402570 629
----
Extremely confused,
-Bernard Liang
推荐答案
如果你发布了你正在编译的实际来源（而不是一些片段）你可以得到一个更合理的答案。
例如，commrate未定义，但类型信息对于
至关重要，看看你是否通过糟糕的sscanf（）格式说明符覆盖了某些东西。
If you post the actual source you are compiling (and not some fragments) you
can get a more reasonable answer.
For instance, commrate is not defined, but the type informationis crucial to
see if you are overwriting something via a bad sscanf() format specifier.
asdf，我以为我收录了所有内容。我猜不会。好吧，这是。
可能有一些不相关的decl''s b / c我正在修改另一个脚本
我写的。但是我认为这里没有什么实质性的东西在这里除了通信定义之外。
#include< stdio.h>
#include< math.h>
#include< float.h>
#include" gpslib。 h"
int main（int argc，char ** argv）{
int pktsize，interval，numgums，p_pktsize，p_interval，p_num;
char trial，p_trial;
int wtf;
double commrate，p_commrate;
int count = 1 ，bufpos = 0，num，i，j; // count =＃of gums
记录，bufpos = fgets缓冲区中的位置
double min = DBL_MAX，max = DBL_MIN，runtot = 0.0;
char buffer [200];
char * bufptr;
FILE * fp;
if（ （argc！= 3）||（（num = atoi（argv [2]））10））{
printf（"％s [stat_file] [num（< = 10）] \ n"，argv [0]）;
返回1;
}
fp = fopen（argv [1]，" r"）;
count = -1;
j = 0;
p_num = -1;
while（fgets（缓冲区，160，fp）！= NULL）{
printf（f ***如何使p_numgums突然变为0 =％d？ ！？！\ n"，p_num）;
wtf = p_num;
sscanf（缓冲区，％d％d％d％1s％* d％lf ;，& pktsize，& interval，& numgums，
& trial，& commrate）;
p_num = wtf;
printf（ok，now what？％d \ n，p_num）;
printf（" from the string |％s"，buffer）;
的printf（QUOT; cur数据集：pktsize =％d interval =％d num =％d trial =％c cmr =％f \ n"，
pktsize，interval，numgums，trial，commrate）;
printf（" prev dataset：pktsize =％d interval =％d num =％d trial =％c cmr =％f \ n"，
p_pktsize，p_interval，p_num ，p_trial，p_commrate）;
if（count == -1）{
count = 1; ++ j;
min = max = runtot = commrate;
}否则if（（p_pktsize == pktsize）&&（p_interval == interval）& &
（p_num == numgums）&&（p_trial == trial））{
++ count; ++ j;
runtot + = commrate;
if（fcompare（commrate，min）< 0）min = commrate;
if （fcompare（max，commrate）< 0）max = commrate;
} else {
printf（"％d \ t％d \ t％d） \t％c \％％d \ t％f \ t％f \ t％f \ n"，
p_pktsize，p_interval，p_num，p_trial，count，runtot / count，max，
min）;
count = 1; j = 1;
min = max = runtot = commrate;
}
p_pktsize = pktsize;
p_interval = interval;
printf（" numgums已从％d更改，p_num）;
p_num = numgums;
printf（"到％d \ n"，p_num）;
p_trial = trial;
p_commrate = commrate;
}
printf（"％d \ t％d \ t％d \ t％\\ t \\ t％\\ t \\ t％\ t \\ t％f \ t％f \ t％f \ n" ;，p_pktsize，p_interval，p_num，
p_trial，count，runtot / count，max，min）;
返回0;
}
Bernard Liang写道：
asdf, I thought I included everything. I guess not. Well here it is.
there might be some irrelevant decl''s b/c I was modifying another script
I had written. but I don''t think there''s anything substantial that is in
here other than the commrate defn''s.
#include <stdio.h>
#include <math.h>
#include <float.h>
#include "gpslib.h"
int main(int argc, char** argv) {
int pktsize, interval, numgums, p_pktsize, p_interval, p_num;
char trial, p_trial;
int wtf;
double commrate, p_commrate;
int count = 1, bufpos = 0, num, i, j; // count = # of gums
recorded, bufpos = position in fgets buffer
double min = DBL_MAX, max = DBL_MIN, runtot = 0.0;
char buffer[200];
char* bufptr;
FILE* fp;
if ((argc != 3) || ((num = atoi(argv[2])) 10)) {
printf("%s [stat_file] [num (<=10)]\n", argv[0]);
return 1;
}
fp = fopen(argv[1], "r");
count = -1;
j=0;
p_num = -1;
while (fgets(buffer, 160, fp) != NULL) {
printf("how the f*** did p_numgums suddenly change to 0=%d?!?!\n", p_num);
wtf = p_num;
sscanf(buffer, "%d %d %d %1s %*d %lf", &pktsize, &interval, &numgums,
&trial, &commrate);
p_num = wtf;
printf("ok, now what? %d\n", p_num);
printf("from the string |%s", buffer);
printf(" cur dataset: pktsize=%d interval=%d num=%d trial=%c cmr=%f\n",
pktsize, interval, numgums, trial, commrate);
printf("prev dataset: pktsize=%d interval=%d num=%d trial=%c cmr=%f\n",
p_pktsize, p_interval, p_num, p_trial, p_commrate);
if (count == -1) {
count = 1; ++j;
min = max = runtot = commrate;
} else if ((p_pktsize == pktsize) && (p_interval == interval) &&
(p_num == numgums) && (p_trial == trial)) {
++count; ++j;
runtot += commrate;
if (fcompare(commrate, min) < 0) min = commrate;
if (fcompare(max, commrate) < 0) max = commrate;
} else {
printf("%d\t%d\t%d\t%c\t%d\t%f\t%f\t%f\n",
p_pktsize, p_interval, p_num, p_trial, count, runtot / count, max,
min);
count = 1; j = 1;
min = max = runtot = commrate;
}
p_pktsize = pktsize;
p_interval = interval;
printf("numgums was changed from %d", p_num);
p_num = numgums;
printf("to %d\n", p_num);
p_trial = trial;
p_commrate = commrate;
}
printf("%d\t%d\t%d\t%c\t%d\t%f\t%f\t%f\n", p_pktsize, p_interval, p_num,
p_trial, count, runtot / count, max, min);
return 0;
}
Bernard Liang wrote:
请考虑以下摘录，附带相关的
声明。
首先，开头标有**，***，****的行不是
应该有的那些明星一开始;他们只习惯直接关注
.
假设，首先，****的行不存在。
p_num以某种方式通过
sscanf命令（***）从之前的值变为0，甚至不涉及p_num。我不能理解它，我怎么可能做任何会修改其值的b / b
。标有**的行被添加以确定那是
确实是导致问题的行。 （之前的值为1，之后的值为0）。
然后我添加了标记为****的行以解决问题，但是是
这种廉价修复的理念非常糟糕的编程风格，
我想知道是否有人可以对此有所了解。
代码如下。
int main（int argc，char ** argv）{
int pktsize，interval，numgums，p_pktsize，p_interval，p_num;
char trial，p_trial;
int wtf;
char buffer [200];
FILE * fp;
fp = fopen（argv [1]，r）;
...
while（fgets（buffer，160，fp）！= NULL）{
** printf（" p_numgums怎么突然变为0 =％d？！？！\ n"，p_num）;
**** wtf = p_num;
*** if（sscanf（缓冲区，％d％d％d％1s％* d％lf，& pktsize，
& interval， & numgums，& trial，& commrate）== 5）{
**** p_num = wtf;
** printf（" ok，now什么？％d \ n"，p_num）;
printf（" from the string |％s"，buffer）;
printf（" cur data set ：pktsize =％d interval =％d num =％d trial =％c cmr =％f \ n"，
pktsize，interval，numgums，trial，commrate）;
printf（" prev data set：pktsize =％d interval =％d num =％d trial =％c cmr =％f \ n"，
p_pktsize，p_interval，p_num，p_trial，p_commrate）;
if（count == -1）{
count = 1; ++ j;
min = max = runtot = commrate;
}否则if（（p_pktsize == pktsize）&&（p_interval ==
interval）&&（p_num == numgums））{
++ count; ++ j;
runtot + = commrate;
if（fcompare（commrate，min）< 0）min = commrate;
if （fcompare（max，commrate）< 0）max = commrate;
} else {
printf（"％d \ t％d \ t％d） \t％c \％％d \ t％f \ t％f \ t％f \ n"，
p_pktsize，p_interval，p_num，p_trial，count，runtot
/ count，max，min）;
count = 1; j = 1;
min = max = runtot = commrate;
}
p_pktsize = pktsize;
p_interval = interval;
printf（" numgums已从％d更改，p_num）;
p_num = numgums;
printf（"到％d \ n"，p_num）;
p_trial = trial;
p_commrate = commrate;
}
}
返回0;
}
我通过argv提供文件的头（-n10） [1]看起来像这样：
----
1000 10 1 a 10 91.041515 1500
1000 10 1 b 11 91.036757 1491
1000 10 1 c 12 87.535014 1500
1000 10 3 a 10 51.517332 859
1000 10 3 a 11 54.095827 910
1000 10 3 a 12 52.226982 890
1000 10 3 b 20 37.465007 629
1000 10 3 b 21 47.486709 786
1000 10 3 b 22 49.602106 829 < br $>
1000 10 3 c 30 36.402570 629
----
非常困惑，
- Bernard Liang
Consider the following excerpt below, with the included relevant
declarations.
Firstly, the lines marked with **, ***, **** at the beginning are not
supposed to have those stars at the beginning; they are only used to
direct attention.
Suppose, first of all, that the lines with the **** are not present.
p_num is somehow getting changed from its previous value to 0 by the
sscanf command (***) that doesn''t even involve p_num. I cannot
understand it, how I could possibly be doing anything that would modify
its value. The lines marked ** were added to determine that that was
indeed the line causing the problem. (the value was 1 before, and 0 after).
I then added the lines marked **** to remedy the problem, but being of
the philosophy that such "cheap fixes" are very poor programming style,
I wanted to see if anyone could shed some insight on this.
Code follows.
int main(int argc, char** argv) {
int pktsize, interval, numgums, p_pktsize, p_interval, p_num;
char trial, p_trial;
int wtf;
char buffer[200];
FILE* fp;
fp = fopen(argv[1], "r");
...
while (fgets(buffer, 160, fp) != NULL) {
**printf("how did p_numgums suddenly change to 0=%d?!?!\n", p_num);
****wtf = p_num;
*** if (sscanf(buffer, "%d %d %d %1s %*d %lf", &pktsize,
&interval, &numgums, &trial, &commrate) == 5) {
****p_num = wtf;
**printf("ok, now what? %d\n", p_num);
printf("from the string |%s", buffer);
printf(" cur data set: pktsize=%d interval=%d num=%d trial=%c cmr=%f\n",
pktsize, interval, numgums, trial, commrate);
printf("prev data set: pktsize=%d interval=%d num=%d trial=%c cmr=%f\n",
p_pktsize, p_interval, p_num, p_trial, p_commrate);
if (count == -1) {
count = 1; ++j;
min = max = runtot = commrate;
} else if ((p_pktsize == pktsize) && (p_interval ==
interval) && (p_num == numgums)) {
++count; ++j;
runtot += commrate;
if (fcompare(commrate, min) < 0) min = commrate;
if (fcompare(max, commrate) < 0) max = commrate;
} else {
printf("%d\t%d\t%d\t%c\t%d\t%f\t%f\t%f\n",
p_pktsize, p_interval, p_num, p_trial, count, runtot
/ count, max, min);
count = 1; j = 1;
min = max = runtot = commrate;
}
p_pktsize = pktsize;
p_interval = interval;
printf("numgums was changed from %d", p_num);
p_num = numgums;
printf("to %d\n", p_num);
p_trial = trial;
p_commrate = commrate;
}
}
return 0;
}
The head (-n10) of the file I am feeding it via argv[1] looks likes this:
----
1000 10 1 a 10 91.041515 1500
1000 10 1 b 11 91.036757 1491
1000 10 1 c 12 87.535014 1500
1000 10 3 a 10 51.517332 859
1000 10 3 a 11 54.095827 910
1000 10 3 a 12 52.226982 890
1000 10 3 b 20 37.465007 629
1000 10 3 b 21 47.486709 786
1000 10 3 b 22 49.602106 829
1000 10 3 c 30 36.402570 629
----
Extremely confused,
-Bernard Liang
Bernard Liang< b _ ***** @ berkeley.eduwrites：
Bernard Liang <b_*****@berkeley.eduwrites:
int pktsize，interval，numgums，p_pktsize，p_interval，p_num;
char trial，p_trial;
int pktsize, interval, numgums, p_pktsize, p_interval, p_num;
char trial, p_trial;
[...]
[...]
*** if（sscanf（buffer，"％d） ％d％d％1s％* d％lf"，& pktsize，
& interval，& numgums，& trial，& commrate）== 5）{
*** if (sscanf(buffer, "%d %d %d %1s %*d %lf", &pktsize,
&interval, &numgums, &trial, &commrate) == 5) {
％1s将存储一个非空格字符和一个终止
％1s或者将试验声明为2个字符的数组。
你没有显示通信声明。它应该有类型
double。
-
有些人*是*傲慢，其他人阅读常见问题解答。
--Chris Dollin
%1s will store one non-white space character plus a terminating
null, but you only allocated room for one byte. Use %c instead
of %1s or declare trial as an array of 2 characters instead.
You didn''t show the declaration of commrate. It should have type
double.
--
"Some people *are* arrogant, and others read the FAQ."
--Chris Dollin
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