LinuxQuestions.org - gcc, segmentation fault, though compiles...

Ok, sorry i was late. I'm providing the whole code here:
NOTE: All the required instructions are on structure OPTAB.

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <ctype.h> //for int toascii(int)
#define opsz 20
#define symsz 1000

struct table{
char symbol[10];
int value;
};
struct table optab[opsz]; //operation table
struct table symtab[symsz]; //Symbol table

//fucntion prototyping
void createoptab(struct table[]);
void initsymtab(struct table[]);
int fetch(char*,char*,char*,char*,char*);
int passone(char*,char*);
int passtwo(char*,char*);

int main(int argc,char* argv[]){
char *str;
char fld1[8],fld2[8],fld3[8],fld4[8];
if(argc<2){
puts("ERR: Syntax. \nPass Source Code as cmdline argument");
exit(0);
}
puts("PASS 1");
passone(argv[1],"FILE.INT");
puts("Intermediate file: FILE.INT");

puts("PASS 2");
passtwo("FILE.INT","FILE.OJB");
puts("Object file: FILE.OJB");
puts("DONE");
return 1;
}

int passtwo(char *inter,char *bin){
FILE *in, *out; //io streams
char fld1[8], fld2[8], fld3[8], fld4[8]; //tmp str for fetch
char loc[8], lbl[8], opc[8], args[8]; //str for respective values
char str[40], buff1[50], buff2[50]; //tmp str during decoding lang.
char tmpstr[30]; //tmpstr
int start, found=0;
int i, count; //tmp
long j, recstart;
in = fopen(inter,"r"); //intermediate file
out= fopen(bin,"w+"); //binary file
puts("\tHeader Record");
//Header Record Processing...
fgets (str, 40, in); //1. get first line of code
fetch (fld1, fld2, fld3, fld4, str); //2. fetch the fields
fprintf(out, "%-1s", "H"); //3. set col1 = H
fprintf(out, "%-6s", fld2); //4. set col2-7= program name, the label with START
start= atoi(fld1);
fprintf(out,"00%-4s\n",itoa(start,tmpstr,16)); //5. set col8-13= starting add of program
puts("\tText Record");
//Text Record Processing...
strcpy(buff1,"\0"); //flushing,
strcpy(buff2,"\0");
count=0;
recstart=start;
while(!feof(in)){ //up to end-of-file
fgets(str,40,in); //fetch line by line
count++; //increment counter of lines
//flushing:
strcpy(loc,"\0"); strcpy(lbl,"\0");
strcpy(opc,"\0"); strcpy(args,"\0");
fetch(fld1,fld2,fld3,fld4,str); //fetch fields
//find loc,lbl,opc,args.
if(fld2[0]==':'){ //contains label
strcpy(loc,fld1); strcpy(lbl,fld2);
strcpy(opc,fld3); strcpy(args,fld4);
}
else{ //no label
strcpy(loc,fld1);
strcpy(opc,fld2);
strcpy(args,fld3);
}
if(!strcmp(opc,"END")){
puts("\nEND encountered");
break; //program ended
}
//find instruction opcode in OPTAB
found=0;
for(i=0;i<opsz;i++) {
if(!strcmp(optab[i].symbol,opc)) { //found
found=1; break;
} //endif
}//endfor

if(found!=0){ //success, OPCODE found in OPTAB.
strcat(buff2,itoa(optab[i].value,tmpstr,16)); //append opcode to buffer buff2
if(strlen(args)>0) //if instruction has argument
{
found=0; //find value of args from symtab
for(i=0;i<symsz;i++){ //serach arg,in symtab.
if(!strcmp(symtab[i].symbol,args))
{found=1; break;}
}
if(found==0) { printf("ERR:Undefined Symbol\n%s %s %s<--",lbl,opc,args);
exit(0);
}
//else:buff2=opcode+arg
if(symtab[i].value>16) //if not a register fill spaces with zeroes
{
if(symtab[i].value>0xfff) strcat(buff2,""); //for 4 digit
else if(symtab[i].value>0xff) strcat(buff2,"0"); //3 digit
else if(symtab[i].value>0xf) strcat(buff2,"00"); //for 2 digit
else strcat(buff2,"000"); //1 digit
} //end filling spaces
//add OPCODE tobuffer.
strcat(buff2,itoa(symtab[i].value,tmpstr,16));
} //endif, with argument.
}// endif opcode found

else{ //OPCODE not found, then it is a directive.
if(!strcmp(opc,"BYTE")){
if(args[0]=='C'||args[0]=='c'){ //if char, convert to ascii value.
for(i=2;i<(strlen(args)-1);i++){ // args[0]=C,[1]=' and arg[n]='
j=toascii(args[i]); //#ctype.h
strcat(buff2,itoa(j,tmpstr,16));
}//end for
}//endif, char*? check
else{ //if number,store the value
j=atoi(args);
if(j<0x10){ //single digit number
strcat(buff2,"0"); //outof 2 col of a byte, fill first by 0
strcat(buff2,itoa(j,tmpstr,16)); //write ascii of number
}
else if(j<0x100){//double digit number
strcat(buff2,itoa(j,tmpstr,16)); //just write in ascii
}
else{//greater than a byte? Possibly error,
printf("ERR: Can't Accomodate in a byte. %d",j);
exit(0);
}
} //end -isnum
}//endif, opc==BYTE

else if(!strcmp(opc,"WORD")){
if(args[0]=='C'||args[0]=='c'){ //if char, convert to ascii value.
for(i=2;i<(strlen(args)-1);i++) // args[0]=C,[1]=' and arg[n]='
{
strcat(buff2,"00"); //char uses 2 byte, fill first 2 byte of word with zeroes.
j=toascii(args[i]); //#ctype.h
strcat(buff2,itoa(j,tmpstr,16));
}//end for
}//endif, char*? check
else{ //if number,store the value
j=atoi(args);
if(j<0x10) strcat(buff2,"000"); //single digit number, outof 4 col of a word, fill 3 by 0s
else if(j<0x100) strcat(buff2,"00");//double digit number, first 2=00
else if(j<0x1000) strcat(buff2,"0"); //3 digit
else if(j<0x10000){/*donothing*/} //4 digit, just write in ascii
else{//greater than a byte? Possibly error,
printf("ERR: Can't Accomodate in a byte. %d",j);
exit(0);
}
strcat(buff2,itoa(j,tmpstr,16)); //now write the number in ascii
} //endelse, number
}//endif, opc==WORD
else if((!strcmp(opc,"RESB"))||(!strcmp(opc,"RESW"))) {} //do nothing
else printf("UNKnERR: Unknown Error in intermediate file\%s not recognized",opc);
}//endelse, OPCODE not found

if((strlen(buff2))>70) //if object code>50 byte, write TEXT Record
{
strcpy(buff1,"T"); //1. col1 = T
//col 2-6, //filling spaces with zeroes.
if(recstart>0xfff) strcat(buff1,"00"); //for 4 digit
else if(recstart>0xff) strcat(buff1,"000"); //3 digit
else if(recstart>0xf) strcat(buff1,"0000"); //for 2 digit
else if(recstart<=0xf) strcat(buff1,"00000"); // 1 digit, including 0

strcat(buff1,itoa(recstart,tmpstr,16)); //2. col 2-6 =start loc of this record, current-6*3
strcat(buff1,itoa(strlen(buff2),tmpstr,16)); //3. col =size of this record
strcat(buff1,buff2); // buff1+=buff2
fprintf(out,"%s\n",buff1);
count=0;
recstart=atoi(loc);
//flush buffers
strcpy(buff1,"\0");
strcpy(buff2,"\0");
}
}//endwhile

if(strlen(buff2)>0) //write the remaining instructioncode, if remaining.
{
strcpy(buff1,"T"); //COL 1

//COL 2-6 //filling spaces with zeroes.
if(recstart>0xfff) strcat(buff1,"00"); //for 4 digit
else if(recstart>0xff) strcat(buff1,"000"); //3 digit
else if(recstart>0xf) strcat(buff1,"0000"); //for 2 digit
else if(recstart<=0xf) strcat(buff1,"00000"); // 1 digit, including 0
strcat(buff1,itoa(recstart,tmpstr,16)); //start loc
strcat(buff1,itoa(strlen(buff2)/2,tmpstr,16)); //object code length of this record
strcat(buff1,buff2);
fprintf(out,"%s",buff1);
}

//end record

fprintf(out,"%s","\nE");
fprintf(out,"00%s",itoa(start,tmpstr,16));

fclose(in);
fclose(out);

puts("Calculating size of object program");
out=fopen(bin,"r+"); //for appending size of object code
fgets(str,40,out); //first string
fseek(out,0,0); //move to first
fseek(out,strlen(str),0); //move to end of this line

// fprintf(out,"FS:%s",itoa(sizeof(out),tmpstr,16)); //write the size.

return 1;
}//ends passtwo()

int passone(char *src,char *inter)
{
FILE *in,*out;
char fld1[8],fld2[8],fld3[8],fld4[8];
char lbl[8],opc[8],args[8];
char str[40];
int LOCCTR,symcnt=9;
int found;
int i; //tmp

in=fopen(src,"r");
out=fopen(inter,"w+");
if(in==NULL){
puts("ERR: Specified source does not exist");
exit(0);
}
createoptab(optab);
initsymtab(symtab);

fgets(str,40,in); //get first ins from in stream
fetch(fld1,fld2,fld3,fld4,str); //fetch fields.
if(fld1[0]==':'){ //has got label
strcpy(lbl,fld1);
strcpy(opc,fld2);
strcpy(args,fld3);
}//endif label
else{ //no label?
strcpy(lbl,"\0");
strcpy(opc,fld1);
strcpy(args,fld2);
} //end else nolabel.
if(!strcmp(opc,"START")) LOCCTR=atoi(args);//if OPCode is START
else{ //if no START,
LOCCTR=0;
fputs("0 :PRG START 0 \n",out);
}
fseek(in,0,0); //move to start
do{
fgets(str,40,in); //get ins line from in stream
fetch(fld1,fld2,fld3,fld4,str); //fetch fields
if(str[0]!='.'){ //if not a .comment continue
fprintf(out,"%s ",itoa(LOCCTR,fld4,10)); //location in DEC.
if(fld1[0]==':'){ //has got label
strcpy(lbl,fld1);
strcpy(opc,fld2);
strcpy(args,fld3);
//Check n UPDATE SYMTAB
for(i=0;i<=symcnt;i++){
if(!strcmp(lbl,symtab[i].symbol)) {
printf("\nERR: Multiple Label Declaration\n%s",lbl);
exit(0);
}//endif, multiple
} //search-end, for loop
//since new label, add to "symtab" and write to intermed. file
strcpy(symtab[symcnt].symbol,lbl);
symtab[symcnt].value=LOCCTR;
symcnt++;
fprintf(out,"%s ",lbl);
} //endif label
else{ //no label
strcpy(lbl,"\0");
strcpy(opc,fld1);
strcpy(args,fld2);
}//end else

found=0; //CHECK INSTRUCTION-validity
for(i=0;i<=opsz;i++){
if(!strcmp(opc,optab[i].symbol)){ //if match found
found=1; break;
}//endif
} //endfor
if(found) LOCCTR+=3;
else if(!strcmp(opc,"WORD")) LOCCTR+=3;
else if(!strcmp(opc,"RESW")) LOCCTR+=atoi(args)*3;
else if(!strcmp(opc,"RESB")) LOCCTR+=atoi(args);
else if(!strcmp(opc,"BYTE")) LOCCTR+=strlen(args);
else if(!strcmp(opc,"START")){} //do nothing now, already done
else if(!strcmp(opc,"END")){} //do nothing
else { printf("\nERR:Unknow Instruction %s",opc);
exit(0);
}
fprintf(out,"%s %s \n",opc,args);//write to file
} //endif .nocomment in line
}while(!feof(in)); //end-of-file encountered.

fclose(in);
fclose(out);
return 1;
}//end passone()

int fetch(char *fld1,char *fld2, char *fld3, char *fld4,char *str)
{
char one[8],two[8],three[8],four[8];
char ch;
int i=0,j=0;
//flushing with null chars
strcpy(one,"\0"); strcpy(two,"\0");
strcpy(three,"\0"); strcpy(four,"\0");

for(;i<strlen(str);i++,j++){ //loop ONE
ch=str[i];
if((ch==32)||(ch=='\t')||(ch=='\n')) { //a white space encountered?
i++; one[j]='\0'; //string terminate
break;
} //endif
one[j]=ch;
} //end for ONE

for(j=0;i<strlen(str);i++,j++) { //loop 4 TWO
ch=str[i];
if((ch==32)||(ch=='\t')||(ch=='\n')) { //white space encounter.
i++; two[j]='\0'; //string terminate
break;
} //endif
two[j]=ch;
} //end for TWO

for(j=0;i<strlen(str);i++,j++) { //loop 4 THREE
ch=str[i];
if((ch==32)||(ch=='\t')||(ch=='\n')) { //White Space?
i++; three[j]='\0'; //string terminate
break;
} //endif
three[j]=ch;
} //endfor THREE

for(j=0;i<strlen(str);i++,j++) { //loop 4 FOUR
ch=str[i];
if((ch==32)||(ch=='\t')||(ch=='\n')) { //a WHITE SPACE
i++; four[j]='\0';//terminate string with NULL
break;
} //endif
four[j]=ch;
} //endfor FOUR
//copy respective fields.
strcpy(fld1,one);
strcpy(fld2,two);
strcpy(fld3,three);
strcpy(fld4,four);
return 1;
}

void createoptab(struct table tab[]){
puts("\tCreating OPTAB...");
strcpy(tab[0].symbol,"ADD"); tab[0].value=0x18;
strcpy(tab[1].symbol,"AND"); tab[1].value=0x40;
strcpy(tab[2].symbol,"CLEAR"); tab[2].value=0xB4;
strcpy(tab[3].symbol,"COMP"); tab[3].value=0x28;
strcpy(tab[4].symbol,"DIV"); tab[4].value=0x24;
strcpy(tab[5].symbol,"J"); tab[5].value=0x3C;
strcpy(tab[6].symbol,"JEQ"); tab[6].value=0x30;
strcpy(tab[7].symbol,"JGT"); tab[7].value=0x34;
strcpy(tab[8].symbol,"JLT"); tab[8].value=0x38;
strcpy(tab[9].symbol,"JSUB"); tab[9].value=0x48;
strcpy(tab[10].symbol,"LDA"); tab[10].value=0x00;
strcpy(tab[11].symbol,"LDL"); tab[11].value=0x08;
strcpy(tab[12].symbol,"MUL"); tab[12].value=0x20;
strcpy(tab[13].symbol,"OR"); tab[13].value=0x44;
strcpy(tab[14].symbol,"RD"); tab[14].value=0xD8;
strcpy(tab[15].symbol,"RSUB"); tab[15].value=0x4C;
strcpy(tab[16].symbol,"STA"); tab[16].value=0x0C;
strcpy(tab[17].symbol,"SUB"); tab[17].value=0x1C;
strcpy(tab[18].symbol,"TIX"); tab[18].value=0x2C;
strcpy(tab[19].symbol,"TD"); tab[19].value=0xE0;
}

void initsymtab(struct table tab[]){
int i;
puts("\tInitializing SYMTAB...");
//flushing
for(i=0;i<100;i++){
strcpy(tab[i].symbol,"\0"); tab[i].value=-1;
}
//Registers and values
strcpy(tab[0].symbol,"A"); tab[0].value=0;
strcpy(tab[1].symbol,"X"); tab[1].value=1;
strcpy(tab[2].symbol,"L"); tab[2].value=2;
strcpy(tab[3].symbol,"PC");tab[3].value=8;
strcpy(tab[4].symbol,"SW");tab[4].value=9;
strcpy(tab[5].symbol,"B"); tab[5].value=3;
strcpy(tab[6].symbol,"S"); tab[6].value=4;
strcpy(tab[7].symbol,"T"); tab[7].value=5;
strcpy(tab[8].symbol,"F"); tab[8].value=6;
}