I want to be able to create a structure record (person name, id number, rating) and save it to a file. I then want to be able to pull the person based on ID number. How? I have tried using the fwrite and fread commands, but I can only "write" one structure at a time. And upon reading it back, I can't seem to pull individual data based on a certain criteria. I'm new at programming, what is it I'm missing about writing and reading info to files??
fread/fwrite(void * data, unsigned packets, size_t size_of_packet, FILE * file)
So ten structs at once would be :
struct Struct array[10];
int size = sizeof(Struct);
int success == fread(array, 10, size, file);
or even:
success == fread(array, 1, size * 10, file);
or even:
success == fread(array, size * 10, 1, file);
or:
while(size == fread(array, 1, size, file))
continue;
So pretty flexible to use these functions. Just read the return value and if is not the same number you passed as the second parameter to fread/fwrite, then an error occured such as end of file, unopened or invalid FILE handles, etc...
Code:#include <cmath> #include <complex> bool euler_flip(bool value) { return std::pow ( std::complex<float>(std::exp(1.0)), std::complex<float>(0, 1) * std::complex<float>(std::atan(1.0) *(1 << (value + 2))) ).real() < 0; }
>>So pretty flexible to use these functions
Unless the structure uses pointers to anonymous memory, such as a name. If this is the case then onlny the value of the pointer will be saved, not the memory it points to. So if your structure looks like this
Then using fread won't work to write any one of the structures to file. You'd have to write each member of each structure manually and read them back manually :-)Code:typedef struct { char *name; long id_num; long rating; } PERSON;
*Cela*
Like hard-coded buffers of known size.
unsigned id;
char name_buffer[128];
char address_buffer[128];
Code:#include <cmath> #include <complex> bool euler_flip(bool value) { return std::pow ( std::complex<float>(std::exp(1.0)), std::complex<float>(0, 1) * std::complex<float>(std::atan(1.0) *(1 << (value + 2))) ).real() < 0; }
