int value changed unexpected - c

Question

I meet a problem of a c program: the int variable is changed unexpected.
Below is all about the problem:
I try to read a txt file which looks like:
2013/12/31 19:53:54, started, /activeJob/start/ Failed
2013/12/31 19:55:55, ended, retCode = 6, Couldn't resolve host name, /activeJob/finish/ Failed
2014/01/01 08:06:55, started, /activeJob/start/ Failed
2014/03/04 12:16:55, started, /activeJob/start/ Success
2014/03/04 12:17:25, ended, retCode = 0, No error, /activeJob/finish/ success
2014/03/04 13:57:21, started, /activeJob/start/ Success
It is a log file which will record the start/finish time of a task. I want to parse the log file and find the finished task record in a order time(latest first). For example, I will try to read the last line and it shows that the task is running. Hence I ignore it and continue to read the last 2nd line. In general the next two line which has "ended" and "started" in pairs can be marked as a record.
My environment is: Centos6.5 (installed via VMWaire).
Below is the source code and it uses libccgi:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "json/json.h"
#include "ccgi.h"
#include <errno.h>
const char *queryName = "account";
const char *queryPage = "pageIndex";
const char *startAction = "/activeJob/start/";
const char *finishAction = "/activeJob/finish/";
const char *contentDes[] = {"there is backup processing, start at :","there is no backup"};
const float pageNums = 8.0;
const char * jsonStringCreate(json_object *jsonObj,int statueCode, char *content, int totalPages)
{
json_object_object_add(jsonObj, "statueCode", json_object_new_int(statueCode));
json_object_object_add(jsonObj, "content", json_object_new_string(content));
json_object_object_add(jsonObj, "totalPages", json_object_new_int((int)totalPages));
//the memory of returned string is under control of jsonObj
return json_object_get_string(jsonObj);
}
char *mallocString(char *string)
{
char *returnString = malloc(sizeof(char) * (1 + strlen(string)));
strcpy(returnString, string);
//owner free the returned string
return returnString;
}
/* File must be open with 'b' in the mode parameter to fopen() */
/* Set file position to size of file before reading last line of file */
char* fgetsr(char* buf, int n, FILE* binaryStream)
{
long fpos;
int cpos;
int first = 1;
if (n < 1 || (fpos = ftell(binaryStream)) == -1 || fpos == 0)
return NULL;
cpos = n - 1;
buf[cpos] = '\0';
for (;;)
{
int c;
if (fseek(binaryStream, --fpos, SEEK_SET) != 0 ||
(c = fgetc(binaryStream)) == EOF)
return NULL;
if (c == '\n' && first == 0) /* accept at most one '\n' */
break;
first = 0;
if (c != '\r') /* ignore DOS/Windows '\r' */
{
unsigned char ch = c;
if (cpos == 0)
{
memmove(buf + 1, buf, n - 2);
++cpos;
}
memcpy(buf + --cpos, &ch, 1);
}
if (fpos == 0)
{
fseek(binaryStream, 0, SEEK_SET);
break;
}
}
memmove(buf, buf + cpos, n - cpos);
return buf;
}
</code></pre>
<pre><code>
int main(int argc, char const *argv[], char **env)
{
int statueCode = 0;
int totalPages = 0;
char *content = NULL;
json_object *jsonObj = json_object_new_object();
printf("Content-type: text/plain; encoding=utf-8\n\n");
CGI_varlist *vl;
const char *name;
CGI_value *value;
int i;
if ((vl = CGI_get_all("/tmp/cgi-upload-XXXXXX") ) == 0)
{
// CGI error
// fputs("CGI_get_all() failed\r\n", stdout);
statueCode = 501;
content = mallocString("CGI error");
}
else
{
//get the CGI env parameters, next to get the query parameter
char *accountName = NULL;
int queryIndex = -1;
for (name = CGI_first_name(vl); name != 0; name = CGI_next_name(vl))
{
value = CGI_lookup_all(vl, 0);
for ( i = 0; value[i] != 0; ++i)
{
if (strcmp(name, queryName) == 0)
{
accountName = malloc(sizeof(char) * (strlen(value[i]) + 4 + 1));
strcpy(accountName, value[i]);
strcat(accountName, ".log");
}
else if (strcmp(name, queryPage) == 0)
{
queryIndex = atoi(value[i]);
}
}
}
if (accountName == NULL || queryIndex < 0)
{
statueCode = 502;
content = mallocString("wrong query parameters format");
}
else
{
//for test, need remove
FILE *logFile = fopen("./test#mail.com.log", "rb");
// FILE *logFile = fopen(accountName, "r");
char *lastLineStr = NULL;
int lineNum = 0;
if (logFile != NULL)
{
//log file is found
char *line = NULL;
size_t len = 0;
ssize_t read;
while( (read = getline(&line, &len, logFile)) != -1)
{
// printf("%s\n", line);
if (strstr(line, finishAction) != 0)
{
/* code */
totalPages ++;
}
lineNum ++;
}
free(line);
int realPage = ceil(totalPages/pageNums);
if (queryIndex > realPage)
{
/* code */
statueCode = 503;
content = mallocString("wrong parameter: query index is beyond the total page");
}
else
{
//log file exist and query index is valid
long startIndex = 0, endIndex = 0, currentIndex = 0;;
startIndex = (queryIndex - 1) * pageNums;
endIndex = (queryIndex) *pageNums;
currentIndex = startIndex;
char buf[256];
int isFinishFound = -1;
int isStartFound = -1;
char *finishContetn[] = {};
char *startContent[] = {};
// this is the core part
while(fgetsr(buf, sizeof(buf), logFile) != NULL && currentIndex lt; endIndex)
{
if (strstr(buf, finishAction) != 0)
{
/* code */
if (isFinishFound > 0)
{
/* code */
continue;
}
else
{
isFinishFound = 1;
isStartFound = -1;
finishContetn[currentIndex] = mallocString(buf);
}
}// strange part:
else if (strstr(buf, startAction) != 0)
{
//finish is not found, means: a start with no finish pairs
if (isFinishFound < 0)
{
/* code */
continue;
}
else
{
if (isStartFound < 0)
{
/* code */
startContent[currentIndex] = mallocString(buf);
isStartFound = 1;
isFinishFound = -1;
currentIndex ++;
}
else
{
continue;
}
}
}
}
}
}
else
{
//log file is not found
statueCode = 400;
content = mallocString("not found the account log");
// printf("not found\n");
// fprintf(stderr, "%d: %s\n", errno, strerror(errno) );
}
if (logFile)
{
fclose(logFile);
}
}
}
return 0;
}
The libjson and libccgi is placed in the right place and I build and make it like:
/usr/local/bin/clang -I /usr/include -DHAVE_SSL -DCLDMAN -DCLDMAN_USE_RETRY -DUSE_PROXY -c -MMD -fPIC -g -DHAVE_SSL -DCLDMAN -I../../build/include -I../../build/include/curl -I../../build/include/json -I../../build/include/svmdisk -o getLog.o getLog.c
/usr/local/bin/clang -o getLog getLog.o -L../../build/lib -lm -lccgi -ljson
and it has no error in the terminal.
The problem I met is the value of int isStartFound will has a strange value of 134538336. It happen when I debug as following:
in the while, the currentIndex=1 which means it begins to find the second record
it finds the "finish", and it begins to do:
isFinishFound = 1;
isStartFound = -1;
finishContetn[currentIndex] = mallocString(buf);
After that, it runs to the while again, and now the isStartFound is changed to 134538336.
I also try to add isStartFound to the watch variable. And it also shows in the "strange part"(which I add in the code) the value of isStartFound changes from -1 to 134538336.
I can't find where this value comes from. I doubt that the way I build and link is wrong. But I failed to find it.
Could any one suggest the way how can I look into?
Thanks!
=======edited:
The problem mainly locates the code below:
char buf[256];
int isFinishFound = -1;
int isStartFound = -1;
while(fgetsr(buf, sizeof(buf), logFile) != NULL && currentIndex 0)
{
continue;
}
else
{
isFinishFound = 1;
isStartFound = -1;
finishContetn[currentIndex] = mallocString(buf);
}
}// here strange happens: the isStartFound changes!
else
{
// other part
}
}
fgetsr is used to read one line of the text; isStartFound&isFinishFound are 2 mask to show whether the "start"/"finish" record is found.
The problem comes with a precondition：the first record is found and now we are try to read the last 5th line(which is the 2nd line). The text file is :
2013/12/31 19:53:54, started, /activeJob/start/ Failed
2013/12/31 19:55:55, ended, retCode = 6, Couldn't resolve host name, /activeJob/finish/ Failed
2014/01/01 08:06:55, started, /activeJob/start/ Failed
2014/03/04 12:16:55, started, /activeJob/start/ Success
2014/03/04 12:17:25, ended, retCode = 0, No error, /activeJob/finish/ success
2014/03/04 13:57:21, started, /activeJob/start/ Success
Now it begins to read the 2nd line and finds "finish", and hence it need to mark the var: isStartFound = -1.
When the program runs to the first "}", the isStartFound is -1. But when it runs to the second "}"(which is the "}" of if (strstr(buf, finishAction) != 0)), the value changes: siStartFound = 134538336!( I add comment in the code) As you can see, here nothing is done!
This is my question and where I feel it weird. (Sorry for the too long code. If this edition still troubles you, please tell me.)

Answer 1

The problem is this declaration:
char *finishContetn[] = {};
This declares finishContetn as an empty array of pointers. Being empty, no matter what index you use to access this array, it will be out of bounds.
As you assign to this array:
finishContetn[currentIndex] = mallocString(buf);
you will write beyond the bounds, and will have undefined behavior. In this case, you will overwrite the stack where other variables are located, like for example the isStartFound variable.
A way to solve this is to either set a fixed size, or to use a dynamic "array". The dynamic array solution requires you to declare the variable as a pointer to pointer (to char) and use realloc to (re)allocate the array.
Something like
char **finishContent = NULL;
size_t finishContentSize = 0; /* Current size of the array */
...
char **temp = realloc(finishContent, sizeof(finishContent[0]) * finishContentSize + 1);
if (temp != NULL)
{
finishContent = temp;
finishContent[finishContentSize++] = malloc(...);
}
Note that I use a temporary variable for the return of realloc, this is because if realloc fails then it won't free finishContent for you, and if you assign directly to finishContent you will loose your original pointer and can't free it later.
Also note that I use sizeof(finishContent[0]). This will work even when finishContent is NULL because sizeof is a pure compile-time operator, it will not create any run-time code.
You might of course need to modify the code to fit your application, but the above should be enough to give you an idea.