Why am I getting a segmentation fault error when searching throught the file the second time?

Question

#include <stdio.h>
#include <fcntl.h>
#include <errno.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <errno.h>
#include <limits.h>
#include <stdlib.h>


#define BUFSIZ 6

In here I search a file for a 3 char code and if the code matches the token it should output what code you entered.

void country_search(char code[6], FILE *dir, FILE *BAC_ptr){

    char *token_off;
    char *token;
    char buf[512];

    while (!feof(dir)){
        if (fgets(buf, 512 , dir)){
            token = strtok(buf,"1234567890");
            while (token != NULL){
                token = strtok(NULL,"1234567890");
                code = strtok(code,"\n");
                if ((strcmp(code,token)) == 0){
                printf("token: %s\n", token);
                }
            }
        }   
    }
}

int main(int argc, const char **argv) {

    char code[6];

    FILE *BAC_ptr;
    BAC_ptr = fopen("BinaryAllCountries.dat", "r");
    FILE *D_ptr;
    D_ptr = fopen("directory.dat", "r");

    fprintf(stdout, "Hello! welcome to the country database press type in: quit[enter] to quit at anytime\n");
    fprintf(stdout, "enter character code of the country you want:\n ");
    fgets(code, BUFSIZ, stdin);

When I use the while loop it asks for the first input then takes it, runs through the country_search() method then comes back, and the 2nd time it gives me a segmentation fault error and I can't figure out why.

        while (strcmp(code, "quit\n") != 0) {
        fprintf(stdout, "enter another character code of the country you want: \n");
            country_search(code, D_ptr, BAC_ptr);
            fgets(code, BUFSIZ, stdin);
        }   
}

here is my directory.dat file

ABW3739AFG1511AGO43AIA3690ALB2635AND2654ANT4227ARE2547ARG5281ARM1532ASM4607ATA1336ATF1392ATG3721AUS4631AUT2675AZE1556BDI170BEL2717BEN62BFA149BGD1600BGR2775BHR1574BHS3759BIH2753BLR2695BLZ3797BMU3816BOL5302BRA5324BRB3778BRN1639BTN1620BVT1357BWA84CAF252CAN3837CCK4691CHE3597CHL5344CHN1684CIV355CMR193COD327COG307COK4715COL5367COM288CPV216CRI3887CUB3906CXR4658CYM3863CYP1703CZE2825DEU2956DJI376DMA3926DNK2846DOM3958DZA22ECU5389EGY396ERI447ESH1275ESP3519EST2867ETH470FIN2913FJI4740FLK5416FRA2934FRO2892FSM4857GAB489GBR3646GEO1745GHA529GIB2975GIN549GLP4044GMB509GNB574GNQ426GRC2996GRD4023GRL4004GTM4068GUF5442GUM4786GUY5459HKG1768HMD1433HND4109HRV2796HTI4087HUN3058IDN1813IND1790IOT122IRL3099IRN1832IRQ1851ISL3078ISR1871ITA3117JAM4130JOR1912JPN1892KAZ1936KEN592KGZ1980KHM1662KIR4806KNA4328KOR2356KWT1956LAO1998LBN2019LBR632LBY668LCA4352LIE3162LKA2380LSO613LTU3185LUX3208LVA3137MAC2037MAR818MCO3288MDA3270MDG691MDV2081MEX4174MHL4834MKD3231MLI731MLT3249MMR2125MNG2103MNP5001MOZ843MRT755MSR4194MTQ4153MUS776MWI712MYS2060MYT796NAM864NCL4900NER884NFK4965NGA907NIC4250NIU4940NLD3314NOR3334NPL2145NRU4874NZL4925OMN2189PAK2213PAN4270PCN5065PER5498PHL2262PLW5018PNG5048POL3355PRI4295PRK2171PRT3377PRY5481PSE2236PYF4769QAT2280REU927ROM3399RUS3433RWA947SAU2307SDN1142SEN1025SGP2330SGS1485SHN970SJM3552SLB5111SLE1073SLV3983SMR3455SOM1095SPM4388STP1004SUR5519SVK3477SVN3499SWE3572SWZ1165SYC1047SYR2400TCA4500TCD270TGO1206THA2468TJK2445TKL5129TKM2513TMP1724TON5146TTO4464TUN1227TUR2487TUV5164TWN2421TZA1188UGA1248UKR3617UMI5208URY5540USA4529UZB2572VAT3036VCT4433VEN5564VGB4555VIR4581VNM2594VUT5228WLF5257WSM5083YEM2614YUG3671ZAF1122ZMB1295

[Why is “while ( !feof (file) )” always wrong?](http://stackoverflow.com/q/5431941/1606345) — David Ranieri, Jan 30 '17 at 21:39
The second time around you are already at the end of that file. — Jongware, Jan 30 '17 at 21:40
`code = strtok(code,"\n");` when `code` is an argument defined as `char code[5]` ? — infixed, Jan 30 '17 at 21:41
Note that you do not `rewind` your files once they have been read (although I don't think that the program crashes for that reason) — Stephan Lechner, Jan 30 '17 at 21:41
`code` only has space for 5 chars, but "quit\n" requires 6 (counting the '\0' and the end). — 001, Jan 30 '17 at 21:41
Why is `BUFSIZ` 6 if the actual size of the buffer is only 5?! — David Schwartz, Jan 30 '17 at 21:48
i have changed it to 6 as @JohnnyMopp made a good point, sorry I didnt mention that — jhowe, Jan 30 '17 at 21:51
@RadLexus when i use the rewind() function i still get the segmentation fault — jhowe, Jan 30 '17 at 21:52
Yes. It was an observation of mine but I could not make it follow through on to a crash -- @StephanLechner is correct in this. — Jongware, Jan 30 '17 at 21:54
Can we see the actual code you are having the problem with then? — David Schwartz, Jan 30 '17 at 21:56
@infixed yea i need to get rid of the \n char as the token will not have one. even if i do get rid of that line the seg. fault still happens — jhowe, Jan 30 '17 at 21:56
@DavidSchwartz, what do u mean? this is the code everything is here. — jhowe, Jan 30 '17 at 21:57
Anyhow, using `strtok` twice that way should not work reliably. But also ... not crash. Hm. — Jongware, Jan 30 '17 at 21:57
@jhowe So `BUFFSIZ` is 6 and the size of the actual buffer is only 5? What's the mystery then? — David Schwartz, Jan 30 '17 at 22:00
Okay, then don't claim you're showing us the actual code you're having the problem with. I looked at it again and it says "`char code[5];`". Can you update your question to show the *actual* code you're having the problem with? And include relevant bits like `BUFSIZ`. — David Schwartz, Jan 30 '17 at 22:03
Your debugger should tell you where the segfault happens. Learn how to use a debugger. It's time now. Really. — Jabberwocky, Jan 30 '17 at 22:08

score 0 · Accepted Answer · answered Jan 30 '17 at 22:11

The program crashes at the following line (valgrind told me right away):

if ((strcmp(code,token)) == 0){

Why? Because you test too soon for a NULL:

    while (token != NULL){
        token = strtok(NULL,"1234567890"); <- right here TOKEN can be set to NULL!
        /* code = strtok(code,"\n"); MUST be moved elsewhere*/
         if ((strcmp(code,token)) == 0){
           printf("token: %s\n", token);
         }

To solve, just insert a NULL check at the appropriate place:

while (token != NULL) {
    token = strtok(NULL,"1234567890");
    if (token)
    {
        if (strcmp(code,token) == 0){ /* no need for extra parens here */
          printf("token: %s\n", token);
        }
    }
}

A few extra remarks:

BAC_PTR is not used.
move the line that removes the \n from code somewhere safe. Preferably outside the loop ... but even better,
entering an empty line will make this crash as well. So remove the \n directly after input, then test for an empty line.
your buffer of 512 is no good. It's too small for the entire directory.dat file, and one of the 3-letter codes gets cut in half.

BAC_ptr will be used just havent gotten there yet and yea i just put 512 for a random number right now will change that thank you. I shall use valgrind I will look it up thank you. — jhowe, Jan 30 '17 at 22:19
@jhowe: it won't harm you to do so, but I've learned how to interpret `valgrind`'s at times cryptic messages. Locate a good debugger – `gdb` sounds just nice for you – so you can step through your code one line at a time, and see variables change value while you do that. — Jongware, Jan 30 '17 at 22:22

Why am I getting a segmentation fault error when searching throught the file the second time?

1 Answers1