Code M.R.E provided.
The symptoms are ' simple ' :
hello\nhello\nhelloEOF & inserting '_' @ ln=2 & col=1 (or rather any line>1 && col==1) the program curiously does it right, but eats up the '\n' , causing line 2 to fuse with line 1 - hello_hello\nhelloEOF , rather than hello\n_hello\nhelloEOF.hello\nhello\nhelloEOF & inserting '_' @ ln=3 & col=5 (or rather at any char col>1 in a line terminated by EOF) results in it skipping the last actual char of the line : hello\nhello\nhell_EOF instead of hello\nhello\nhell_oEOF.col==1 in line terminated by EOF)results in the error message (\n Invalid Index.) being thrown.As far as my intuition is concerned, I reckon a flaw when dealing with line termination ('\n',EOF) & how it is counted, as well as loop counters in general, but I'm not getting it.
The idea/algorithm :
EOF.The code below does all the real talking :
#include <stdio.h>
#include <string.h>
/* Likely error region in chknmove(), chkncpy() and/or main() ;
All other functions used are also provided */
long long lncnt(FILE *lcount){
/* counts the number of lines in a file with fgets() */
rewind(lcount); /* ensures lines counted from beginning */
long long lines=0; char line[501];
while((fgets(line,501,lcount))!=NULL){
lines++;
}
rewind(lcount); /* leaves fptr @ 0,0 rather than EOF */
return lines;
}
int chknmove(FILE *tomove, long long line, long long col){
/* Function to check & move FILE* to certain line/col */
rewind(tomove); /* make sure fptr is at beginning of file */
int f=0; /* set check-variable to 0 for successful */
if(line<1 || col<1)
f = -1; /* Ln,col cannot be -ve or even 0 -> 1st col is @ 1ln,1col in any non-empty file */
else{
long long i,q; i=1;q=0; /* i = lines seen, q = cols seen */
/* i init to 1 for ease of comprehension v/s testing 'line-1' */
while(i<line || q<col){ /* loop must iterate until i==line && q==col */
int ch = fgetc(tomove); /* int to store EOF */
if(ch==EOF){
f=-1; break; /* if file ends before reaching index, failed. */
}
else if(ch=='\n') {
if(i==line){
f=-1; break;/* if line ends before reaching col in ln, failed. */
}
i++; q=0; /* else , increase i by 1 and set q (col) to 0 */
}
else
q++; /* any other character is 'normal' , just increment q (col) by 1 */
}
}
if(f==0){
fseek(tomove,-1,SEEK_CUR);
/* since index must be checked, loop reaches it -> fseek(-1) causes *next* r/w to fptr to be on the index . */
return 0;
}
else{
/* f != 0 : moving has failed. */
printf("\n Invalid Index.\n");
return -1;
}
}
int chkncpy(FILE *source, FILE *dest,long long beginln, long long begincol, long long endln, long long endcol){
rewind(source); int f=0;
if(beginln<1 || begincol<1 || endln<beginln || endcol<1 || (beginln==endln && endcol<begincol))
f=-1; /* line/col must be >= 1 in non-empty file, copying done top to bottom (begin-index <= end-index ) */
else{
if(chknmove(source,beginln,begincol)==0){
/* loop begins if begin-index is valid */
long long i,q; i=beginln;q=begincol; /* i = lines, q = cols */
while(i<endln || q<endcol){
/* while end-index is not reached : !(i==endln && q==endcol) */
int ch = fgetc(source);
if(ch==EOF) {f=-1; break;} /* File ends b/w begin-index & end-index - failed. */
else if(ch=='\n') {
if(i==endln) {f=-1; break;} /* endln ends before reaching endcol - failed */
i++; q=0;
fputc(ch,dest); /* valid '\n' put in dest file */
}
else{
q++; fputc(ch,dest); /* valid char put in dest file */
}
}
}
else f=-1; /* if begin-index is invalid, failed. */
}
if(f==-1){
/* if f != 0 : chkncpy() failed */
printf("\n Invalid Index.\n");
return -1;
}
else /* if f remains == 0 */ return 0;
}
long long lastlncol(FILE *fyl){
rewind(fyl); /* makes sure fptr @ beginning */
chknmove(fyl,lncnt(fyl),1); /* move to last line */
long long cnt=0; /* cnt stores no. of chars in last line */
while(1){
int g = fgetc(fyl);
if (g==EOF)
break; /* EOF not counted */
else if(g=='\n'){
cnt++;break; /* \n is counted as a char, but also as EOL */
}
else
cnt++; /* all other chars counted */
}
rewind(fyl); /* leaves file at its beginning */
return cnt;
}
long long lcc(FILE *fyl,long long line){
rewind(fyl); int f = chknmove(fyl,line,1); /* moves fptr to line */
long long cnt=0;
if(f==0){
while(1){
int g = fgetc(fyl);
if (g==EOF)
break;
else if(g=='\n'){
cnt++;break;
}
else
cnt++;
}
rewind(fyl);
return cnt;
}
else
return -1;
}
void writer(FILE *write, int ctrl){
printf("\n Terminate Input with \"/end/\".\n\n Type below :\n\n");
char in[501]; /* str that stores input line-by-line */
char *p; int o;
while(1){
fgets(in,501,stdin); /* takes line from user */
if((p=strstr(in,"/end/"))!=0){
/* if line has "/end/", all chars till /end/ are written to file and input loop breaks */
o = p-in;
fprintf(write,"%.*s",o,in);
break;
}
else{
/* writes line to file */
fputs(in,write);
}
}
if(ctrl==0){
/* in some cases, file must not be closed yet , hence ctrl is taken */
int s = fclose(write);
if(s==EOF) printf("\n Error ");
else printf("\n Success.\n");
}
}
void eat() /* clears stdin */
{
int eat;while ((eat = getchar()) != '\n' && eat != EOF);
}
int main(){
/* main to add/insert to file @ given index */
char fadd[501];/* filename str */
printf("\n Filename : "); scanf("%500[^\n]",fadd);
FILE * add = fopen(fadd,"r");
if(add==NULL)
perror("\n Error "); /* if file does not pre-exist */
else{
long long line, col; char sep; printf("\n Index : "); scanf("%lld%c%lld",&line,&sep,&col); /* takes index in ln-char-col form */
eat(); /* clears stdin */
FILE * tmp=fopen("Temp.Ctt","w"); /* opens a tmp file to write */
if(tmp==NULL)
perror("\n Error "); /* failed - tmp file could not be created to write */
else{
int f; /* success var */
if(line==1 && col>1){
/* if user wants to insert @ a col>1 in line 1 */
f = chkncpy(add,tmp,1,1,line,col); /* all below calls intend to write till 1 char before the char @ given index */
}
else if(line>1 && col>1){
/* if user wants to insert @ a col>1 in any line>1*/
f = chkncpy(add,tmp,1,1,line,col-1);
}
else if(line>1 && col==1){ //ERRORS - ignores the '\n' of line-1
/* if user wants to insert @ a 1st col in line>1 */
f = chkncpy(add,tmp,1,1,line-1,lcc(add,line-1));
}
else if(line==1 && col==1){
/* if user wants to insert @ 1,1 (no moving/copying needed) */
f=0;
}
else{
printf("\n Invalid Index.\n");f=-1;
}
if(f==0){
writer(tmp,1);
/* calls function to allow user to write to fptr , with ctrl != 0, so writer() *won't* fclose(tmp) */
chkncpy(add,tmp,line,col,lncnt(add),lastlncol(add));
/* copies all characters from index till EOF */
int ok = fclose(tmp); fclose(add);
if(ok==EOF){
/* if closing tmp was unsuccessful, the file on disk may be corrupted/incomplete, so must be removed */
remove("Temp.Ctt");perror("\n Error ");
}
else{
if(rename("Temp.Ctt",fadd)==0)
printf("\n Success.\n");
else{
/* on Windows & some other non-POSIX systems, file cannot be renamed to pre-existing filename , hence delete original */
remove(fadd);
if(rename("Temp.Ctt",fadd)==0)
printf("\n Success.\n");
else{
/* if rename still unsuccessful, throw an error, remove tmp file and give up */
remove("Temp.Ctt");
perror("\n Error ");
}
}
}
}
}
}
}
In case of any missing details or inadvertent errors, please comment and I will correct them.
This is my self-answer , issues with chknmove() and chkncpy() were resulting in ' glitching ', those have been fixed below.
The below is ready-to-compile , and generously commented and spaced, and hence is actually larger than the main idea, which is encapsulated in chknmove() and chkncpy() - so these have been placed at the top of the code.
Hope this question/answer is useful to others in the future.
#include <stdio.h> // For file & console I/O
#include <string.h> // For strstr() in writer()
int chknmove(FILE *tomove, long long line, long long col){
/* Moves FILE* to given ((line,col) -1 char) , such that next char read from FILE* will be @ (line,col)
Checks validity of index as it moves : if col not in line || EOF encountered, returns -1. */
rewind(tomove); // rewind file 'just in case'
int f = 0 ; // control variable which stores state (succeeded/failed) of chknmove()
if (line < 1 || col < 1)
{
f=-1;
printf("\n Illegal Index.\n");
// Follows 1-based line/col index : -ve values are illegal
return -1;
}
else {
long long i,q; i = q = 0; // i = lines encountered ; q = chars encountered in line i ; both are 0-based
while(i < line){
int chk = fgetc(tomove); //
if(chk == EOF){
printf("\nInvalid %s - beyond EOF.\n", (i == line -1 ) ? "Column" : "Line");
f = -1; break;
}
else if(chk == '\n'){
if(i==line-1 && q == col-1)
/* 1. This allows for user to directly point to the '\n' char , allowing him to append to line
2.(line/col - 1) : since i & q are 0-based */
break;
else{
if(i == line-1 ){
// except if target index was the '\n' , reading beyond newline @ target line is invalid, since '\n' terminates line
printf("\nInvalid column for line %lld.\n",line);
f=-1; break;
}
i++; q=0; // if not @ target line , reset and continue
}
}
else if(i == line-1 && q == col-1 ) // if dest index reached, break .
break;
else // if non-EOF , non-\n char encountered, increment q and continue.
q++;
}
if(f==0){
fseek(tomove,-1,SEEK_CUR); // So that the after returning/exiting chknmove() , the char read from FILE* is @ line,col
return 0;
}
else
return -1;
}
}
int chkncpy(FILE* source, FILE *dest, long long beginln, long long begincol, long long endln, long long endcol) {
/* Copies everything from FILE *source to FILE *dest within begining index and terminating index , if they're valid
Returns -1 if they're invalid.*/
if (beginln < 1 || begincol < 1 || endln < beginln || endcol < ((endln == beginln) ? begincol : 1))
// -ve indexes and reading/writing backwards is illegal
return -1;
long long i, q; // i -> lines && q -> chars
int f=0;
if(chknmove(source,beginln,begincol)==0){
// checked if begining index is valid and if so, moved to it.
i=beginln; q=begincol; // i & q have same base as line & col , so 1-based
while(1){
int ch = fgetc(source);
if(ch==EOF){
printf("\nInvalid Terminating Index.\n");
f=-1; break;
}
else if(ch=='\n'){
if(i==endln && q==endcol){
fputc(ch,dest);
break;
}
else{
if(i==endln){
printf("Invalid column for line %lld.\n",endln);
f=-1; break;
}
i++; q=1; // q set to 1 -> q is 1-based !
fputc(ch,dest);
}
}
else if(i==endln && q==endcol){
fputc(ch,dest); break;
}
else{
q++; fputc(ch,dest);
}
}
}
else
f=-1;
if(f==0) return 0;
else return -1;
}
long long lcc(FILE *fyl,long long line){
// L.C.C. == line char count , i.e, count of chars in a line (including the \n).
int f = chknmove(fyl,line,1); /* attempt moving to line, store returned val */
long long cnt=0; // cnt -> number of chars found
if(f==0){ // if line exists , then :
while(1){
int g = fgetc(fyl);
if (g==EOF) // EOF checked in case line is last line
break;
else if(g=='\n'){ // '\n' is EOL , hence it is counted and then loop is terminated .
cnt++; break;
}
else
cnt++;
}
rewind(fyl);
return cnt;
}
else
return -1; // if line doesn't exist, return -1
}
int clone(FILE *wfrm,FILE *wto){
// clones wfrom ("Write From ") onto wto ("Write To") until EOF is encountered.
while(1){
int a =fgetc(wfrm);
if(a==EOF)
break;
else
fputc(a,wto);
}
return 0;
}
void writer(FILE *write){
// Allows basic console line-level I/O for writing to FILE *
printf("\n Terminate Input with \"/end/\".\n\n\tType below :\n\n");
char in[501]; /* str that stores input line-by-line */
char *p; int o;
while(1){
fgets(in,501,stdin); /* takes line from user */
if((p=strstr(in,"/end/"))!=0){
/* if line has "/end/", all chars till /end/ are written to file and input loop breaks */
o = p-in;
fprintf(write,"%.*s",o,in);
break;
}
else{
/* writes line to file */
fputs(in,write);
}
}
}
void eat() /* clears stdin */
{
int eat;while ((eat = getchar()) != '\n' && eat != EOF);
}
int main(){
/* main to add/insert to file @ given index */
char fadd[501]=""; // String to store fname
printf("\n Filename : "); scanf("%500[^\n]",fadd); eat(); // Take fname, clear stdin .
FILE * add = fopen(fadd,"r"); // open file
if(add==NULL)
perror("\n Error ");
else{
// If File is loaded for reading successfully
long long line, col; char sep; // line, col and seperating char make up the index
printf("\n Index : "); scanf("%lld%c%lld",&line,&sep,&col); eat(); // take index, clear stdin
FILE * tmp=fopen("Temp.Ctt","w"); // open a temporary file
if(tmp==NULL)
perror("\n Error ");
else{
int f;
if(line>=1 && col>1){ // copy till the line , col-1
f = chkncpy(add,tmp,1,1,line,col-1);
}
else if(line>1 && col==1){ // copy till line-1 , last char
f = chkncpy(add,tmp,1,1,line-1,lcc(add,line-1));
}
else if(line==1 && col==1){ // no moving/copying necessary at all
f=0;
}
else{
printf("\n Invalid Index.\n");f=-1;
}
if(f==0){ // if Index was not invalid
writer(tmp); // let user write to temp file
clone(add,tmp); //clones the rest of add to tmp - both are *not* fclosed
int ok = fclose(tmp); fclose(add);
if(ok==EOF){
/* if closing tmp was unsuccessful, the file on disk may be corrupted/incomplete, so must be removed */
remove("Temp.Ctt");perror("\n Error ");
}
else{
if(rename("Temp.Ctt",fadd)==0)
printf("\n Success.\n");
else{
/* on Windows & some other non-POSIX systems, file cannot be renamed to pre-existing filename , hence delete original */
remove(fadd);
if(rename("Temp.Ctt",fadd)==0)
printf("\n Success.\n");
else{
/* if rename still unsuccessful, throw an error, point user to temp file and give up */
perror("\n Error ");
printf("\n %s lost. File-buffer exists as %s in cwd.\n",fadd,"Temp.Ctt");
}
}
}
}
else
remove("Temp.Ctt");
}
}
return 0;
}
Any constructive critique which may improve the answer is welcome. In case of any inadvertent errors or missing details, please comment and I will reply ASAP.