snprintf overflows and prints garbage to file randomly. help-Collection of common programming errors
Here is my code, basically one the 4 computer I have tested it on they all work perfectly with very large data sizes, eg textfiles up to 500mb in size, but when I run them on the server with real data even files as small as 6mb seem to overrun somewhere and writes garbage to the end of my files.
Here is the source of the entire function so people can have a more indepth look
/** Reads values from tagname between start_time and end_time which are strings in the format
of 01/01/1970-12:00, a null string is treated as 01/01/1970, values are stored in
"tagname".csv */
int ReadValues(char * tagname, char * start_time, char * end_time, char * working_directory, char * new_tag_name)
{
long lRet;
int number_of_samples;
int loop;
IHU_DATA_SAMPLE * pSamples=NULL;
IHU_TIMESTAMP StartTime;
IHU_TIMESTAMP EndTime;
FILE *stream;
char outputFileName[200];
char szQuality[100];
char newTempTagName[100];
int Year;
int Month;
int Day;
int Hour;
int Minute;
int Second;
long Subsecond;
int date[10];
//if we want to change the tagname do it now
if(new_tag_name != 0){
strncpy(newTempTagName, new_tag_name, 100);
} else {
strncpy(newTempTagName, tagname, 100);
}
// if the tagname contains a character that is invalid for a filename then we have to make a name
if ( (strstr(newTempTagName, "/")) || (strstr(newTempTagName, "\\")) || (strstr(newTempTagName, ":")))
{
sprintf(outputFileName, "MadeUpTag%d", MadeUpTagCount++);
}
else
{
//If a working directory was passed in use it
if(!working_directory){
strncpy(outputFileName, newTempTagName,199);
} else {
strcpy(outputFileName, working_directory); //Copy the working directory to the filename
// Append a / on the end of the working directory if it doesn't already have one
if(outputFileName[strlen(outputFileName)-1] == '\"'){
outputFileName[strlen(outputFileName)-1] = 0;
}
if(outputFileName[strlen(outputFileName)-1] != '\\'){
strncat(outputFileName, "\\", 199);
}
strncat(outputFileName, newTempTagName, 199); //Copy the tagname to the end of the working directory
}
}
//Add the csv file extension
strcat(outputFileName, ".csv");
#ifdef DEBUG
printf("Output filename: %s\n", outputFileName);
#endif
stream = fopen(outputFileName, "w");
if( stream == NULL ) {
printf("The file %s can not be opened\n", outputFileName );
} else {
//If start_time == 0 we want to start at 1970
if(start_time == 0){
// we want all the data so use an old start time
struct tm local;
local.tm_year = date[2] - 1900;
local.tm_mon = date[1] - 1;
local.tm_mday = date[0];
local.tm_hour = date[3];
local.tm_min = date[4];
local.tm_sec = 0;
time_t utc_seconds = mktime(&local);
StartTime.Seconds = (long)utc_seconds;
StartTime.Subseconds = 0;
} else {
//we have been supplied a start time
#ifdef DEBUG
printf("Start Time: ");
#endif
lRet = convert_date(start_time, &StartTime);
#ifdef DEBUG
printf("Seconds %ld \n", StartTime.Seconds);
#endif
}
//if end_time == 0 we want to go all the way until now.
if(end_time == 0){
// end time of 0 means now
memset(&EndTime, 0, sizeof(EndTime));
} else {
//we have been supplied an end time
#ifdef DEBUG
printf("End Time: ");
#endif
lRet = convert_date(end_time, &EndTime);
#ifdef DEBUG
printf("Seconds %ld \n", EndTime.Seconds);
#endif
}
// API will determine actual samples that are in that time range
number_of_samples=0;
// API will allocate the memory
pSamples = NULL;
//timeTaken();
lRet = ihuReadRawDataByTime
(
serverhandle, // the handle returned from the connect
tagname, // the single tagname to retrieve
&StartTime, // start time for query
&EndTime, // end time for query
&number_of_samples, // will be set by API
&pSamples // will be allocated and populated in the user API
);
char temp[100];
char Header[100];
char lengthOfHeader = 0;
char SampleAndTag[100];
int lengthOfSampleAndTag = 0;
char ActualSample[100];
int lengthOfActualSample = 0;
char NumberOfSamples[100];
int lengthOfNumberOfSamples = 0;
int oldQualityStatus = 99999;
if (lRet == ihuSTATUS_OK)
{
// successful read
lengthOfHeader = snprintf(Header, 100, "[Data]\nTagname,TimeStamp,Value,DataQuality\n");
if(lengthOfHeader < 0){
printf("ERROR WRITING TO BUFFER!\n");
} else {
if(fwrite(Header, 1, lengthOfHeader, stream) < lengthOfHeader){
printf("ERROR WRITING TO FILE!\n");
}
}
for (loop = 0;loop < number_of_samples;loop++)
{
struct tm * local;
local = localtime(&pSamples[loop].TimeStamp.Seconds);
Month = local->tm_mon + 1;
Day = local->tm_mday;
Year = local->tm_year + 1900;
Hour = local->tm_hour;
Minute = local->tm_min;
Second = local->tm_sec;
Subsecond = pSamples[loop].TimeStamp.Subseconds;
//lengthOfSampleAndTag = snprintf(SampleAndTag, 100, "Sample %d, %s",loop, newTempTagName);
lengthOfSampleAndTag = snprintf(SampleAndTag, 100, "%s", newTempTagName);
if(lengthOfSampleAndTag < 0){
printf("ERROR WRITING TO BUFFER!\n");
} else {
if(fwrite(SampleAndTag, 1,lengthOfSampleAndTag, stream) < lengthOfSampleAndTag){
printf("ERROR WRITING TO FILE!\n");
}
}
//Doing the formatting ourselves manually per character saves about 20% of cpu time
//on large databases this can save hours
temp[0] = ',';
temp[1] = ' ';
temp[2] = Month/10 + 0x30; //Tens
temp[3] = Month%10 + 0x30; //units
temp[4] = '/';
temp[5] = Day/10 + 0x30;
temp[6] = Day%10 + 0x30;
temp[7] = '/';
temp[8] = Year/1000 + 0x30;
temp[9] = '0';
temp[10] = (Year%100)/10 + 0x30;
temp[11] = (Year%100)%10 + 0x30;
temp[12] = ' ';
temp[13] = Hour/10 + 0x30; //Tens
temp[14] = Hour%10 + 0x30; //units
temp[15] = ':';
temp[16] = Minute/10 + 0x30;
temp[17] = Minute%10 + 0x30;
temp[18] = ':';
temp[19] = Second/10 + 0x30;
temp[20] = Second%10 + 0x30;
temp[21] = '.';
temp[22] = '0';
temp[23] = '0';
temp[24] = '0';
temp[25] = ',';
temp[26] = ' ';
temp[27] = 0; //Null termination
//This is to save copying the string if it is the same
if(oldQualityStatus != pSamples[loop].Quality.QualityStatus){
oldQualityStatus = pSamples[loop].Quality.QualityStatus;
switch(pSamples[loop].Quality.QualityStatus)
{
case ihuOPCBad:
strncpy(szQuality,"Bad",99);
break;
case ihuOPCUncertain:
strncpy(szQuality,"Uncertain",99);
break;
case ihuOPCNA:
strncpy(szQuality,"NotAvailable",99);
break;
case ihuOPCGood:
strncpy(szQuality,"Good",99);
break;
default:
strncpy(szQuality,"Really unknown",99);
break;
}
}
if ( pSamples[loop].ValueDataType == ihuFloat )
{
//lengthOfActualSample = snprintf(ActualSample, 100,"%s%8.7f, %s, Type:Float\n",temp,pSamples[loop].Value.Float,szQuality);
lengthOfActualSample = snprintf(ActualSample, 100,"%s%8.7f, %s\n",temp,pSamples[loop].Value.Float,szQuality);
if(lengthOfActualSample < 0){
printf("ERROR WRITING TO BUFFER!\n");
} else {
if(fwrite(ActualSample, 1, lengthOfActualSample, stream) < lengthOfActualSample){
printf("ERROR WRITING TO FILE!\n");
}
}
}
else if ( pSamples[loop].ValueDataType == ihuDoubleFloat )
{
//lengthOfActualSample = snprintf(ActualSample, 100,"%s%8.15f, %s, Type: DoubleFloat\n ",temp,pSamples[loop].Value.DoubleFloat,szQuality);
lengthOfActualSample = snprintf(ActualSample, 100,"%s%8.15f, %s\n ",temp,pSamples[loop].Value.DoubleFloat,szQuality);
if(lengthOfActualSample < 0){
printf("ERROR WRITING TO BUFFER!\n");
} else {
if(fwrite(ActualSample, 1,lengthOfActualSample, stream) < lengthOfActualSample){
printf("ERROR WRITING TO FILE!\n");
}
}
}
else if ( pSamples[loop].ValueDataType == ihuShort )
{
//lengthOfActualSample = snprintf(ActualSample, 100,"%s%d, %s, Type:Short\n",temp,pSamples[loop].Value.Short,szQuality);
lengthOfActualSample = snprintf(ActualSample, 100,"%s%d, %s\n",temp,pSamples[loop].Value.Short,szQuality);
if(lengthOfActualSampleOriginally posted 2013-11-09 23:23:03.