c - Invalid Read of size 1 on running Valgrind -

c - Invalid Read of size 1 on running Valgrind -

the next error got after running valrind valgrind --tool=memcheck --leak-check=full --show-reachable=yes ./out ==12140== invalid read of size 1 ==12140== @ 0x4c2df84: strncat (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so) ==12140== 0x40100d: createsortedruns (final.c:178) ==12140== 0x401297: main (final.c:249) ==12140== address 0x51fd549 0 bytes after block of size 9 alloc'd ==12140== @ 0x4c2ab80: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so) ==12140== 0x400efd: createsortedruns (final.c:150) ==12140== 0x401297: main (final.c:249) ==12140==

the other error getting is:

==12140== invalid write of size 1 ==12140== @ 0x4c2dfd0: strncat (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so) ==12140== 0x40100d: createsortedruns (final.c:178) ==12140== 0x401297: main (final.c:249) ==12140== address 0x51fd54d 4 bytes after block of size 9 alloc'd ==12140== @ 0x4c2ab80: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so) ==12140== 0x400efd: createsortedruns (final.c:150) ==12140== 0x401297: main (final.c:249) ==12140== ==12140== ==12140== 250 errors in context 7 of 13:

the other error getting is:

==12140== invalid read of size 1 ==12140== @ 0x4c2df84: strncat (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so) ==12140== 0x40100d: createsortedruns (final.c:178) ==12140== 0x401297: main (final.c:249) ==12140== address 0x51fd549 0 bytes after block of size 9 alloc'd ==12140== @ 0x4c2ab80: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so) ==12140== 0x400efd: createsortedruns (final.c:150) ==12140== 0x401297: main (final.c:249) ==12140==

the next snippet of program:

void createsortedruns(int start, int end, char file[]){ file *givenfile = null; givenfile=fopen(file,"r+b"); rewind(givenfile); int i=0; /*printf("file:%s\n",file); printf("file length:%zu\n",strlen(file));*/ char *temp = (char *)malloc(sizeof(char)*strlen(file)); for(i=start; i<end; i++){ fseek(givenfile,0,seek_cur); fread(&inputbuffer[act_inputbuffersize],sizeof(int),1,givenfile); act_inputbuffersize++; if((act_inputbuffersize==max_inputbuffersize) ||(i==(end-1))){ //sort qsort(inputbuffer,act_inputbuffersize,sizeof(int),compare); // write file strncpy(temp,file,strlen(file)); //int k=0; char counter[4]={0}; /*for(k=0;k<4;k++){ counter[k]=0; }*/ snprintf(counter,5, ".%03d", totalsortedfiles); counter[strlen(counter)] = '\0'; strncat(temp,counter,4); file *int_file = null; int_file=fopen(temp,"w+b"); rewind(int_file); fwrite(&inputbuffer,sizeof(int),act_inputbuffersize,int_file); // register sub_fo info small_fo=register_sub_fo(small_fo,totalsortedfiles,temp, 0 ,act_inputbuffersize,act_inputbuffersize); // increment totalsortedfiles totalsortedfiles+=1; // reinitialize int j=0; for(j=0;j<max_inputbuffersize;j++){ inputbuffer[j]=0; } act_inputbuffersize=0; int len = strlen(temp); temp[len-4] = '\0'; // garbage fclose(int_file); int_file = null; } } //for_end fclose(givenfile); givenfile=null; free(temp); temp=null; } // func_end

valgrind showing error @ line "strncat(temp,counter,4);" can please explain me error ?

strncpy function not zero-terminate target buffer if size limit reached during copying. using strncpy in code , reaches size limit

strncpy(temp,file,strlen(file));

this means @ point temp not zero-terminated. temp not string after strncpy call.

after do

strncat(temp,counter,4);

but strncat requires first operand string. in case not string. behavior undefined.

as has been stated many times, strncpy not limited-length string copying function. using such error prone , lame. if can made "work", still not right tool job.

in add-on that, buffer allocated temp cannot accommodate more characters in add-on there after strncpy. buffer allocated strlen(file) characters long.

also, statement not seem create sense @ ll

counter[strlen(counter)] = '\0';

in order strlen work, counter must zero-terminated. so, doing re-terminating counter string @ exact location @ terminated. point of that?

you don't need that. snprintf produced zero-terminated string.

however, snprintf invocation problematic itself.

char counter[4]={0}; snprintf(counter,5, ".%03d", totalsortedfiles);

your counter array declared size 4. passing 5 buffer size snprintf lying snprintf. in general case snprintf go out of bounds. behavior undefined.

the format used in snprintf suggests need buffer of size 5.

c gdb valgrind