C++ Random Access Files -

its first time experiment random access files in c++ however, i've tried before in java can't work in c++. idea want create 100 empty records, , store record @ particular record number in file. here code, kept simple possible.

i have here structure named tool:

struct tool {     int number;     char name[20];     int quantity;     double cost; }; 

and here have in main function:

fstream outfile; outfile.open("inventory.dat");  // create 100 empty tool records tool tool; tool.number = 0; tool.name[0] = '\0'; tool.quantity = 0; tool.cost = 0;    (int = 0; < 100; i++) {     outfile.write(reinterpret_cast<char *>(&tool.number), sizeof(int));     outfile.write(tool.name, sizeof(char)* 20);     outfile.write(reinterpret_cast<char *>(&tool.quantity), sizeof(int));     outfile.write(reinterpret_cast<char *>(&tool.cost), sizeof(double)); }  // insert tool record tool t; t.number = 3; t.quantity = 7; t.cost = 57; strcpy(tool.name, "electric sander");  outfile.seekp((tool.number - 1) * sizeof(tool)); outfile.write(reinterpret_cast<char *>(&tool.number), sizeof(int)); outfile.write(tool.name, sizeof(char)* 20); outfile.write(reinterpret_cast<char *>(&tool.quantity), sizeof(int)); outfile.write(reinterpret_cast<char *>(&tool.cost), sizeof(double));  outfile.close(); 

the part initialize 100 empty record works fine (assuming comment insert section of code.

however, when insert section performed, program generates 4 gb of data. i'm not sure what's going on. appreciate kind of help. in advance.

you write entire contents of struct

    outfile.seekp(t.number*sizeof(tool));     outfile.write(reinterpret_cast<char *>(&tool),sizeof(tool)); 

don´t forget tell compiler don´t insert padding

#ifdef msvc #pragma pack(push,1) #endif struct tool {     int number;     char name[20];     int quantity;     double cost; #ifdef gcc }__attribute__((packed)); #else }; #endif  #ifdef msvc #pragma pack(pop) #endif 

sources:
https://codereview.stackexchange.com/questions/26344/writing-reading-data-structure-to-a-file-using-c
https://stackoverflow.com/a/18654265/194717
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