I'm trying to update a record of a random access file in C. I just need to update the integer cant_discos in every record of my .dat file.
This is the code i wrote, i have 2 problems:
1) My code just let me edit the first record of my file.
2) The program doesn't update the record.
typedef struct{
int codigo;
char nombre[30];
char integrantes[100];
int cant_discos;
} t_bandas;
int main()
{
int res,cant;
t_bandas aux;
FILE * fd;
fd=fopen("bandas.dat","rb+");
if(fd==NULL){ puts("ERROR"); exit(-1)}
while(!feof(fd)){
res=fread(&aux,sizeof( t_bandas),1,fd);
if(res!=0){
printf("New cant value..\n");
scanf("%d",&cant);
aux.cant_discos=cant;
fwrite(&aux,sizeof( t_bandas),1,fd);
}
}
fclose(fd);
return 0; }
fseek
should be called when switching between read and write.
#include <stdio.h>
#include <stdlib.h>
typedef struct{
int codigo;
char nombre[30];
char integrantes[100];
int cant_discos;
} t_bandas;
int main()
{
int res,cant;
long pos = 0;
t_bandas aux;
FILE * fd;
fd=fopen("bandas.dat","rb+");
if(fd==NULL){
puts("ERROR");
exit(-1);
}
while ( ( res = fread ( &aux, 1, sizeof ( t_bandas), fd)) == sizeof ( t_bandas)) {
printf("New cant value..\n");
scanf("%d",&cant);
aux.cant_discos=cant;
fseek ( fd, pos, SEEK_SET);//seek to start of record
fwrite(&aux,sizeof( t_bandas),1,fd);
pos = ftell ( fd);//store end of record
fseek ( fd, 0, SEEK_CUR);//seek in-place to change from write to read
}
fclose(fd);
return 0;
}