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);
}









share|improve this question























  • 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.

    – xing
    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.

    – xing
    Nov 25 '18 at 21:30
















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);
}









share|improve this question























  • 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.

    – xing
    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.

    – xing
    Nov 25 '18 at 21:30














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);
}









share|improve this question














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






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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. Then fprintf(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 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.

    – 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











  • 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.

    – xing
    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.

    – 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.

– xing
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.

– xing
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.

– xing
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.

– xing
Nov 25 '18 at 21:30












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