I'm having the famous segmentation fault. I've tracked it down to a single line in the code (getline). Here's someone with a similar issue, also on Ubuntu:
http://www.daniweb.com/software-development/cpp/threads/329191
Note that getline returns -1 after the segmentation fault, but it couldn't have been really the end of the stream (in my case).
When the stream is smaller, everything goes ok. As we can deduce from the output, the segmentation fault is on line 98.
1 /*
2 * File: RequestDispatcher.cpp
3 * Author: albert
4 *
5 * Created on July 8, 2011, 7:15 PM
6 */
7
8 #include "iostream"
9 #include "fstream"
10 #include "stdlib.h"
11 #include "stdio.h"
12 #include "cstring"
13 #include "algorithm"
14
15 #include "RequestDispatcher.h"
16 #include "Functions.h"
17
18 #define PROXIES 1
19
20 RequestDispatcher::RequestDispatcher()
21 {
22 }
23
24 RequestDispatcher::RequestDispatcher(const RequestDispatcher& orig)
25 {
26 }
27
28 RequestDispatcher::~RequestDispatcher()
29 {
30 }
31
32 int RequestDispatcher::addRequest(string host, string request, IResponseReceiver* response_receiver)
33 {
34 RequestInfo info;
35 info.request_index = request_info.size();
36 info.host = host;
37 info.request = request;
38 info.response_receiver = response_receiver;
39 request_info.push_back(info);
40 return info.request_index;
41 }
42
43 void RequestDispatcher::run()
44 {
45 if (request_info.size()==0)
46 {
47 return;
48 }
49 FILE* pipe[PROXIES];
50 int per_proxy = (request_info.size() + PROXIES - 1) / PROXIES;
51 int count_pipes = (request_info.size() + per_proxy - 1) / per_proxy;
52 for (int pipe_index=0; pipe_index<count_pipes; ++pipe_index)
53 {
54 int from = pipe_index * per_proxy;
55 int to = min(from + per_proxy, int(request_info.size()));
56 cout << "FROM: "<< from << "; TO: " << to;
57 const char* cmd = generateCmd(from, to);
58 pipe[pipe_index] = popen(cmd, "r");
59 if (!pipe[pipe_index])
60 {
61 cerr << "Error executing command in RequestDispatcher::run()";
62 }
63 }
64 string result[PROXIES];
65 bool finished[PROXIES];
66 for (int pipe_index=0; pipe_index<count_pipes; pipe_index++)
67 {
68 finished[pipe_index] = false;
69 }
70 int count_finished = 0;
71 char* buffer;
72 size_t buffer_length=1024;
73 buffer = (char *) malloc (buffer_length + 1);
74 while (count_finished < count_pipes)
75 {
76 cout << "D\n";
77 fflush(stdout);
78 for(int pipe_index=0; pipe_index<count_pipes; ++pipe_index)
79 {
80 cout << "E\n";
81 fflush(stdout);
82 if (finished[pipe_index])
83 {
84 continue;
85 }
86 cout << "Getline" << buffer_length << "\n";
87 ssize_t bytes_read = getline(&buffer, &buffer_length, pipe[pipe_index]);
88 cout << "Getline Done ("<<bytes_read<< "," << buffer_length << ")\n";
89 fflush(stdout);
90 while (bytes_read>0)
91 {
92 for (int i=0; i<bytes_read; i++)
93 {
94 result[pipe_index] += buffer[i];
95 }
96 cout << "P\n";
97 fflush(stdout);
98 bytes_read = getline(&buffer, &buffer_length, pipe[pipe_index]);
99 cout << "Bytes read ("<<bytes_read<<","<< buffer_length << ")\n";
100 fflush(stdout);
101
102 }
103 if (bytes_read == -1) // then finished this pipe
104 {
105 string* r = &result[pipe_index];
106 //cout << *r;
107 finished[pipe_index] = true;
108 ++count_finished;
109 cout << "HI\n";
110 fflush(stdout);
111 // delete trailing '\0' from result
112 pclose(pipe[pipe_index]);
113 result[pipe_index] = result[pipe_index].substr(0, result[pipe_index].length()-1);
114 int pos = r->find("RESPONSE_DATA");
115 int valuepos, endvaluepos;
116 int request_index, length;
117 string headers;
118 int headerslength;
119 string body;
120 int bodypos, bodylength;
121 while (pos!=r->npos)
122 {
123 valuepos = r->find("REQUEST_INDEX=", pos) + 14;
124 endvaluepos = r->find("\n", valuepos);
125 request_index = pipe_index * per_proxy + atoi(r->substr(valuepos, endvaluepos-valuepos).c_str());
126
127 cout << "REQUEST_INDEX " << request_index;
128
129 valuepos = r->find("LENGTH=", pos) + 7;
130 endvaluepos = r->find("\n", valuepos);
131 length = atoi(r->substr(valuepos, endvaluepos-valuepos).c_str());
132
133 pos = r->find("START", pos)+5;
134 bodypos = r->find("\r\n\r\n", pos)+4;
135 headerslength = bodypos-pos-4;
136 bodylength = length-headerslength-4;
137 headers = r->substr(pos, headerslength);
138 body = r->substr(bodypos, bodylength);
139 request_info[request_index].response_receiver->notifyResponse(headers, body, request_index);
140
141 pos=r->find("RESPONSE_DATA", pos+length);
142 }
143 }
144 }
145 }
146 cout << "\n?\n";
147 fflush(stdout);
148 free(buffer);
149 request_info.clear();
150 }
151
152 const char* RequestDispatcher::generateCmd(int first_request, int to_request)
153 {
154 string r("/home/albert/apachebench-standalone-read-only/ab -a");
155 for (int i=first_request; i<to_request; i++)
156 {
157 r.append(" '");
158 r.append(request_info.at(i).request);
159 r.append("'");
160 }
161 ofstream out("/home/albert/apachebench-standalone-read-only/debug");
162 if(! out)
163 {
164 cerr<<"Cannot open output file\n";
165 return "";
166 }
167 out << r.c_str();
168 out.close();
169 return "/home/albert/apachebench-standalone-read-only/debug";
170 /*int size = strlen("/home/albert/apachebench-standalone-read-only/ab -a");
171 for (int i=first_request; i<to_request; i++)
172 {
173 size += 2+strlen(request_info.at(i).request)+1;
174 cout << "len: " << strlen(request_info.at(i).request) << "\n";
175 cout << "total: " << size << "\n";
176 }
177 size += 1;
178 char* cmd = new char[size];
179 strcpy(cmd, "/home/albert/apachebench-standalone-read-only/ab -a");
180 for (int i=first_request; i<to_request; i++)
181 {
182 cout << "LEN: " << strlen(cmd) << "\n";
183 cout << "NEXT: " << strlen(request_info.at(i).request) << "\n";
184 fflush(stdout);
185 strcat(cmd, " '");
186 strcat(cmd, request_info.at(i).request);
187 strcat(cmd, "'");
188 }
189 cout << "LEN: " << strlen(cmd) << "\n";
190 fflush(stdout);
191 return cmd;*/
192 }
When I run /home/albert/apachebench-standalone-read-only/debug from the command line everything works perfectly fine. It returns binary data.
The end of the output is:
P
Bytes read (272,6828)
P
Bytes read (42,6828)
P
Bytes read (464,6828)
P
Bytes read (195,6828)
P
Bytes read (355,6828)
P
Bytes read (69,6828)
P
Bytes read (111,6828)
P
Segmentation fault
Bytes read (368,6828)
P
Bytes read (-1,6828)
HI
REQUEST_INDEX 46REQUEST_INDEX 48REQUEST_INDEX 44REQUEST_INDEX 0REQUEST_INDEX 45
?
Mind the "?" for exiting the loop. After this, the program is finished.
By the way, I always thought the program would terminate on a segmentation fault (edit: I did not do anything to catch it).
In reply to some answers: There seem to be different versions of getline and I seem to be using the one documented here:
http://www.kernel.org/doc/man-pages/online/pages/man3/getline.3.html
So after some thought the issue I believe is that your buffer is being written to as you're reading it. In some cases the buffer is not done being written to and you remove some of the data from it (which could mean that you may read an empty buffer because the write isn't done). This is because you are using popen and simply piping data from another process. What I would recommend is that for one you use the C++ standard for getline (although both are somewhat unsafe) and that you have some leeway for reading data from the pipe. Retry logic might be what you need as I can't think of a clean way to solve this. If anyone knows please post it, I'm posting this because this is what I believe to be the likely culprit of the problem.
Also if you're coding in C++ I highly recommend that you use the C++ libraries so that you're not constantly mixing or casting between types (such as string to char * and such, it just saves you some hassle) and that you use the safer versions of methods so you avoid errors such as buffer overflows.
Related
I wrote a program to print the sum of first 25 natural numbers using a recursive function.
It went fine and I also got the correct output(ie 325).
After that I played a little with my code just to see what happens.
Here is the code :
int su(int sum,int i)
{
if(i<26)
{
sum=sum+i+su(sum,i+1);
cout << sum << endl; // I added this line to see what happens.
// This line wasn't needed but I still
// added it.
}
else
return sum;
}
When I ran this code, it printed weird values of the variable sum.
Here is a screenshot the output : output
The sum of first 25 natural numbers is 325 but that doesn't even show up anywhere in the output. Instead, I got different numbers as in my output.
However when I remove the line cout << sum << endl; from the if statement, I get the expected sum (ie 325).
What is the cause of that?
Your non-void function does not return anything when i is less than 26 and this is undefined behavior. If you checked/turned on the compiler warnings you would see the warning:
warning: control reaches end of non-void function [-Wreturn-type]
}
^
Removing the already pointless else fixes that issue:
#include <iostream>
using namespace std;
int su(int sum,int i)
{
if(i<26)
{
sum=sum+i+su(sum,i+1);
cout<<sum<<endl;
}
// Removed the else. Always returns something
return sum;
}
int main() {
std::cout << su(0, 0) <<std::endl;
}
Output:
25
49
72
94
115
135
154
172
189
205
220
234
247
259
270
280
289
297
304
310
315
319
322
324
325
325
325
Always firstly make sure your recursive function eventually gets out of the loop and returns a value in case it's not void. A much simpler and cleaner way would be like this (a bit like the classic factorial function):
#include <iostream>
int sum (int i) {
if(i == 1) {
return 1;
}
return i + sum(i-1);
}
int main() {
std::cout << sum(25) <<std::endl;
}
Output:
325
If you add std::cout to see what's going on under the hood:
#include <iostream>
int sum (int i) {
std::cout << i << std::endl; // current integer
if(i == 1) {
return 1;
}
return i + sum(i-1);
}
int main() {
std::cout << sum(25) <<std::endl;
}
The output is as expected:
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
325
Your function doesn't return anything if not at the end of the recursion. Remove the else keyword it should work.
I am trying to execute scsi inquiry command.
I managed to do it with:
device_ = open(device_path, O_RDWR|O_NONBLOCK);
...
if (ioctl(device, SG_IO, &io_hdr) < 0)
{
int err = errno;
cerr << "Inquiry SG_IO ioctl error. Errno: " << err <<
"; error message: " << strerror(err) << endl;
result = false;
}
How should I rewrite my code to use write/read pair instead?
SG_IO is a blocking operation, it ignores O_NONBLOCK flag and I need to be sure that the call will not block.
I used these articles as a reference:
http://www.tldp.org/HOWTO/SCSI-Generic-HOWTO/write.html
http://www.tldp.org/HOWTO/SCSI-Generic-HOWTO/read.html
...and wrote such code:
sg_io_hdr_t io_hdr, out_io_hdr;
do
{
size_t count = sizeof(sg_io_hdr_t);
size_t written = write(device, &io_hdr, count);
if (written == count)
{
break;
}
int err = errno;
cerr << "write io_hdr_t. Errno: " << err << "; error message: " << strerror(err) << endl;
if (err != EAGAIN)
{
return false;
}
} while (true);
do
{
size_t count = sizeof(sg_io_hdr_t);
// same result with both io_hdr and out_io_hdr as a second parameter
size_t read_count = read(device, &out_io_hdr, count);
if (read_count == count)
{
break;
}
int err = errno;
cerr << "write io_hdr_t. Errno: " << err << "; error message: " << strerror(err) << endl;
if (err != EAGAIN)
{
return false;
}
} while (true);
But this code results in a trash in a status fields as well as in a sense buffer:
INQUIRY sense data length: 100
inquiry sense buffer (hex):
e4 9a eb 2a 30 fa de 2a 20 0
0 0 40 91 e6 2a d8 c3 e0 2a
40 5 f3 2a 14 38 e6 2a 14 38
e6 2a 0 0 0 0 3 0 0 0
0 0 0 0 1 0 0 0 b4 eb
b1 7f 1 0 0 0 e8 4e e6 2a
b8 eb b1 7f 0 0 41 0 5c ec
b1 7f 78 3c 40 0 2b 0 0 0
14 38 e6 2a 34 eb b1 7f 0 0
0 0 0 0 0 0 2 0 0 0
INQUIRY SCSI status=0xfe
masked_status=0x13
INQUIRY host_status=0x3f47
INQUIRY driver_status=0x93c8
How do I make iconv do conversions to UTF-* encodings without adding a byte order mark?
The problem is shown by this code, compiled with G++ 4.8 under 64-bit Linux:
#include <iostream>
#include <iconv.h>
#include <cstdint>
#include <iomanip>
using namespace std;
int main() {
const wchar_t *ws = L"Hello, world.\n";
for(size_t ii = 0; ii < 15; ii++) {
cout << setw(2) << hex << uint32_t(ws[ii]) << " ";
}
cout << endl;
iconv_t conv = iconv_open("UTF-16", "UTF-32");
char *outbuf = new char[14 * 4];
char *inptr = const_cast<char*>(reinterpret_cast<const char *>(ws));
char *outptr = outbuf;
size_t in_len = 14 * 4;
size_t out_len = 14 * 4;
size_t result = iconv(conv, &inptr, &in_len, &outptr, &out_len);
uint16_t *encoded = reinterpret_cast<uint16_t*>(outbuf);
for(size_t ii = 0; ii < 15; ii++) {
cout << setw(2) << hex << encoded[ii] << " ";
}
cout << endl;
}
This outputs:
48 65 6c 6c 6f 2c 20 77 6f 72 6c 64 2e a 0
feff 48 65 6c 6c 6f 2c 20 77 6f 72 6c 64 2e a
clearly showing the BOM at the start of the resulting string where it is not present at the
I found that this works for me:
iconv_t conv = iconv_open("UTF16LE", "UTF32");
Though I believe it's implementation-dependent.
There is a similar question: Using iconv to convert from UTF-16BE to UTF-8 without BOM
I've been trying to find reverse relations between jobs. To be more specific I will tell it with an example.
Suppose I have n jobs i.e {0,1,2,3,4,...n}. I also have relations between jobs. I know only successor jobs, i.e., 2 is followed by 4,5. 5 is followed by 7,8 etc. I have it in a text file. I want to obtaing precedence relations between jobs (what is the predecessor job of 5?).
Having text output would be great. I have some code but it does not work.
#include <iostream>
#include <fstream>
#include <iomanip>
#include <cstdlib>
#include <ctime>
using namespace std;
#define TOTAL_ACTIVITY 123
void readFile();
void change ();
void writeFile ();
struct Activity {
int precedessor [3];
int successor [3];
int id;
};
Activity activityList[TOTAL_ACTIVITY];
void main() {
readFile();
change();
writeFile();
}
void readFile() {
ifstream myReadFile;
myReadFile.open("pre.txt");
if (!myReadFile) { //check whether the file can be opened
cerr << "Unable to open file"; // terminate with error
}
while (!myReadFile.eof()) {
int Id,suc1, suc2, suc3;
int t = 0;
while (myReadFile >> Id >> suc1 >> suc2 >> suc3) //data should be in this order
{
activityList[t].id = Id;
activityList[t].successor [0] = suc1;
activityList[t].successor [1] = suc2;
activityList[t].successor [2] = suc3;
t++;
}
}
return;
}
void change() {
int act;
for (int i=1;i<TOTAL_ACTIVITY;i++){
for (int j=0;j<TOTAL_ACTIVITY;j++){
for (int k=0;k<3;k++) {
if (activityList[j].successor[k]==i;)
}
}
}
}
void writeFile() {
ofstream out("out.txt");
out << "id\t" << "Pre1\t" << "Pre2\t" << "Pre3\t"<<"\n";
for (int j = 0; j < TOTAL_ACTIVITY; j++) {
out << activityList[j].id << "\t";
out << activityList[j].precedessor[0]<< "\t";
out << activityList[j].precedessor[1] << "\t";
out << activityList[j].precedessor[2] << "\t";
out << "\n";
}
out.close();
}
Here is a sample input:
ID Successor1 Successor2 Successor3
1 2 3 4
2 6 11 15
3 7 8 13
4 5 9 10
5 20
6 30
7 27
8 12 19 27
9 14
10 16 25
11 20 26
12 14
13 17 18
14 17
15 25
16 21 22
17 22
18 20 22
19 24 29
20 23 25
21 28
22 23
23 24
24 30
25 30
26 31
27 28
28 31
29 32
30 32
31 32
Output should be something like this:
Id Predecesor1 Predecesor2 Predecesor3
........................................
...........................................
...........................................
You are given the successors of a job, but you do not need to retain this information.
For example, if I say: 5 -> 6, 7 meaning that 5 is followed by 6 and 7, then it is equivalent to saying that 6 and 7 are preceded by 5, right.
You can then either:
directly output the precedence when reading the successors
store in an associative container, using the job id as the key and the predecessor as value
Specifics details... are for you to work out to conclude your homework.
I'm in trouble using std::string::find(). I read strings from console through the following code:
50 while(command.find(exitString) != 0) {
51 std::cout << "$ ";
52 getline(std::cin, command);
53
54 doSwitch(command);
55 }
and then I "switch" on them, through the following function:
59 void Console::doSwitch(std::string command) {
60 if(command.find(helpString) == 0) {
61 help();
62 } else if(command.find(loadString) == 0) {
63 try {
64 doLoad(command);
65 } catch(std::string str) {
66 std::cout << str << std::endl;
67 }
68 } else if(command.find(dumpProcString) == 0) {
69 try {
70 doDumpProc(command);
71 } catch(std::string str) {
72 std::cout << str << std::endl;
73 }
74 } else if(command.find(dumpMemString) == 0) {
75 doDumpMem();
76 } else if(command.find(defmemString) == 0) {
77 try {
78 doDefmem(command);
79 } catch(std::string str) {
80 std::cout << str << std::endl;
81 } catch(char *str) {
82 std::cout << str << std::endl;
83 }
84 } else if(command.find(resetString) == 0) {
85 try {
86 doReset();
87 } catch(std::string str) {
88 std::cout << str << std::endl;
89 }
90 } else {
91 std::cout << "Comando inválido." << std::endl;
92 }
93 }
but sometimes it simply doesn't switch correctly. Any clues?
Thanks in advance,
EDIT:
I've done some tests and I detected it was falling on the last else-if statement, instead of falling on the last else.
Then I checked my code again and found that the root cause was that I forgot to initialize resetString.
Problem solved!
Thank you everyone.
You might be expecting that find returns zero when it found the string, kind of like the way strcmp works.
But that's not how find works. find returns the first index of the found string, which might be zero, or might be something else if the string you're looking for is prepended with spaces, other strings, etc.
If find doesn't find what you're looking for, it returns string::npos. So your if...else block should be checking to find if the strings were found or not found, not checking to see if they were at index zero. Like this:
if(command.find(helpString) != string::npos ) {
help();
} else if /// ... etc...
You are reading a line and then calling doSwitch() without checking if its exitString. In that case, when the input is exitString, else block at the end of doSwitch() function is executed, causing the program to print "Command Invalido" before exiting the loop.
Is this what you observed?
If its something else, please let us know for what input your code behaves incorrectly and what is the input and output.