Rewrite file in C using fseek
1
I read text from a file line by line and split the strings with strtok, after that I put them into a array of pointer and wanted to rewrite the outputline in the same file.
For the first line it does work, but for the other lines - there is always the first character missing in the output textfile. I guess there must be something wrong with the position of the file pointer, but I don't get it.
int main(void){
long pos = 0;
char *token=NULL;
char *list_text[100];
char array[100]={0};
FILE *file;
file = fopen("list.txt", "r+");
pos = ftell(file);
//read file in line by line
while(fgets(array,100,file) != NULL){
int i = 0;
int j = 0;
//split string
token = strtok(array," ");
while(token != NULL) {
printf("Token: %sn", token);
list_text[i++] = token;
token = strtok(NULL," ");
j++;
}
//rewrite in file
fseek(file, pos, SEEK_SET);
for (int i= 0; i < j; i++){
fprintf(file, "%s ", list_text[i]);
}
fflush(file);
pos = ftell(file);
for (int i = 0; i < j; i++){ //reset
list_text[i] = 0;
}
}
fclose(file);
return(EXIT_SUCCESS);
}
c file url-rewriting fseek
asked Nov 25 '18 at 19:52
LaviLavi
62
add a comment |
1
I read text from a file line by line and split the strings with strtok, after that I put them into a array of pointer and wanted to rewrite the outputline in the same file.
For the first line it does work, but for the other lines - there is always the first character missing in the output textfile. I guess there must be something wrong with the position of the file pointer, but I don't get it.
int main(void){
long pos = 0;
char *token=NULL;
char *list_text[100];
char array[100]={0};
FILE *file;
file = fopen("list.txt", "r+");
pos = ftell(file);
//read file in line by line
while(fgets(array,100,file) != NULL){
int i = 0;
int j = 0;
//split string
token = strtok(array," ");
while(token != NULL) {
printf("Token: %sn", token);
list_text[i++] = token;
token = strtok(NULL," ");
j++;
}
//rewrite in file
fseek(file, pos, SEEK_SET);
for (int i= 0; i < j; i++){
fprintf(file, "%s ", list_text[i]);
}
fflush(file);
pos = ftell(file);
for (int i = 0; i < j; i++){ //reset
list_text[i] = 0;
}
}
fclose(file);
return(EXIT_SUCCESS);
}
c file url-rewriting fseek
asked Nov 25 '18 at 19:52
LaviLavi
62
you should seek before each read & each write (related/duplicate: stackoverflow.com/questions/53344969/…)
– Jean-François Fabre
Nov 25 '18 at 19:59
strtok(NULL," ")will leave the newline as part of the last token. Thenfprintf(file, "%s ",may write the newline and an additional space that overwrites the first character of the next line.
– xing
Nov 25 '18 at 20:13
Added a check usingstrchrto see if the token contained a newline. If so, just print the tokenfprintf(file, "%s",otherwise print the token and a space. Fixed the problem for me on Linux.
– xing
Nov 25 '18 at 21:30
add a comment |
1
1
1
I read text from a file line by line and split the strings with strtok, after that I put them into a array of pointer and wanted to rewrite the outputline in the same file.
For the first line it does work, but for the other lines - there is always the first character missing in the output textfile. I guess there must be something wrong with the position of the file pointer, but I don't get it.
int main(void){
long pos = 0;
char *token=NULL;
char *list_text[100];
char array[100]={0};
FILE *file;
file = fopen("list.txt", "r+");
pos = ftell(file);
//read file in line by line
while(fgets(array,100,file) != NULL){
int i = 0;
int j = 0;
//split string
token = strtok(array," ");
while(token != NULL) {
printf("Token: %sn", token);
list_text[i++] = token;
token = strtok(NULL," ");
j++;
}
//rewrite in file
fseek(file, pos, SEEK_SET);
for (int i= 0; i < j; i++){
fprintf(file, "%s ", list_text[i]);
}
fflush(file);
pos = ftell(file);
for (int i = 0; i < j; i++){ //reset
list_text[i] = 0;
}
}
fclose(file);
return(EXIT_SUCCESS);
}
c file url-rewriting fseek
asked Nov 25 '18 at 19:52
LaviLavi
62
I read text from a file line by line and split the strings with strtok, after that I put them into a array of pointer and wanted to rewrite the outputline in the same file.
For the first line it does work, but for the other lines - there is always the first character missing in the output textfile. I guess there must be something wrong with the position of the file pointer, but I don't get it.
int main(void){
long pos = 0;
char *token=NULL;
char *list_text[100];
char array[100]={0};
FILE *file;
file = fopen("list.txt", "r+");
pos = ftell(file);
//read file in line by line
while(fgets(array,100,file) != NULL){
int i = 0;
int j = 0;
//split string
token = strtok(array," ");
while(token != NULL) {
printf("Token: %sn", token);
list_text[i++] = token;
token = strtok(NULL," ");
j++;
}
//rewrite in file
fseek(file, pos, SEEK_SET);
for (int i= 0; i < j; i++){
fprintf(file, "%s ", list_text[i]);
}
fflush(file);
pos = ftell(file);
for (int i = 0; i < j; i++){ //reset
list_text[i] = 0;
}
}
fclose(file);
return(EXIT_SUCCESS);
}
c file url-rewriting fseek
c file url-rewriting fseek
asked Nov 25 '18 at 19:52
LaviLavi
62
asked Nov 25 '18 at 19:52
LaviLavi
62
asked Nov 25 '18 at 19:52
LaviLavi
62
asked Nov 25 '18 at 19:52
LaviLavi
62
asked Nov 25 '18 at 19:52
LaviLavi
62
62
you should seek before each read & each write (related/duplicate: stackoverflow.com/questions/53344969/…)
– Jean-François Fabre
Nov 25 '18 at 19:59
strtok(NULL," ")will leave the newline as part of the last token. Thenfprintf(file, "%s ",may write the newline and an additional space that overwrites the first character of the next line.
– xing
Nov 25 '18 at 20:13
Added a check usingstrchrto see if the token contained a newline. If so, just print the tokenfprintf(file, "%s",otherwise print the token and a space. Fixed the problem for me on Linux.
– xing
Nov 25 '18 at 21:30
add a comment |
you should seek before each read & each write (related/duplicate: stackoverflow.com/questions/53344969/…)
– Jean-François Fabre
Nov 25 '18 at 19:59
strtok(NULL," ")will leave the newline as part of the last token. Thenfprintf(file, "%s ",may write the newline and an additional space that overwrites the first character of the next line.
– xing
Nov 25 '18 at 20:13
Added a check usingstrchrto see if the token contained a newline. If so, just print the tokenfprintf(file, "%s",otherwise print the token and a space. Fixed the problem for me on Linux.
– xing
Nov 25 '18 at 21:30
you should seek before each read & each write (related/duplicate: stackoverflow.com/questions/53344969/…)
– Jean-François Fabre
Nov 25 '18 at 19:59
you should seek before each read & each write (related/duplicate: stackoverflow.com/questions/53344969/…)
– Jean-François Fabre
Nov 25 '18 at 19:59
strtok(NULL," ") will leave the newline as part of the last token. Then fprintf(file, "%s ", may write the newline and an additional space that overwrites the first character of the next line.Nov 25 '18 at 20:13
strtok(NULL," ") will leave the newline as part of the last token. Then fprintf(file, "%s ", may write the newline and an additional space that overwrites the first character of the next line.Nov 25 '18 at 20:13
Added a check using
strchr to see if the token contained a newline. If so, just print the token fprintf(file, "%s", otherwise print the token and a space. Fixed the problem for me on Linux.Nov 25 '18 at 21:30
Added a check using
strchr to see if the token contained a newline. If so, just print the token fprintf(file, "%s", otherwise print the token and a space. Fixed the problem for me on Linux.Nov 25 '18 at 21:30
add a comment |
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you should seek before each read & each write (related/duplicate: stackoverflow.com/questions/53344969/…)
– Jean-François Fabre
Nov 25 '18 at 19:59
strtok(NULL," ")will leave the newline as part of the last token. Thenfprintf(file, "%s ",may write the newline and an additional space that overwrites the first character of the next line.– xing
Nov 25 '18 at 20:13
Added a check using
strchrto see if the token contained a newline. If so, just print the tokenfprintf(file, "%s",otherwise print the token and a space. Fixed the problem for me on Linux.– xing
Nov 25 '18 at 21:30