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write and read string to binary file C++

To write a std::string to a binary file, you need to save the string length first: std::string str(“whatever”); size_t size=str.size(); outfile.write(&size,sizeof(size)); outfile.write(&str[0],size); To read it in, reverse the process, resizing the string first so you will have enough space: std::string str; size_t size; infile.read(&size, sizeof(size)); str.resize(size); infile.read(&str[0], size); Because strings have a variable size, unless … Read more

Should I check if malloc() was successful?

This mainly only adds to the existing answer but I understand where you are coming from, if you do a lot of memory allocation your code ends up looking very ugly with all the error checks for malloc. Personally I often get around this using a small malloc wrapper which will never fail. Unless your … Read more

Find malloc() array length in C? [duplicate]

In the second case, num is not an array, is a pointer. sizeof is giving you the size of the pointer, which seems to be 8 bytes on your platform. There is no way to know the size of a dynamically allocated array, you have to save it somewhere else. sizeof looks at the type, … Read more

How big can a malloc be in C?

Observations Assuming a typical allocator, such as the one glibc uses, there are some observations: Whether or not the memory is actually used, the region must be reserved contiguously in virtual memory. The largest free contiguous regions depends on the memory usage of existing memory regions, and the availability of those regions to malloc. The … Read more

If free() knows the length of my array, why can’t I ask for it in my own code?

Besides Klatchko’s correct point that the standard does not provide for it, real malloc/free implementations often allocate more space then you ask for. E.g. if you ask for 12 bytes it may provide 16 (see A Memory Allocator, which notes that 16 is a common size). So it doesn’t need to know you asked for … Read more

Why, or when, do you need to dynamically allocate memory in C?

You need to use dynamic memory when: You cannot determine the maximum amount of memory to use at compile time; You want to allocate a very large object; You want to build data structures (containers) without a fixed upper size; You don’t always know how much memory you will need to set aside at compile … Read more

malloc implementation?

The easiest way to do it is to keep a linked list of free block. In malloc, if the list is not empty, you search for a block large enough to satisfy the request and return it. If the list is empty or if no such block can be found, you call sbrk to allocate … Read more

malloc(sizeof(int)) vs malloc(sizeof(int )) vs (int )malloc(sizeof(int))

malloc(sizeof(int)) means you are allocating space off the heap to store an int. You are reserving as many bytes as an int requires. This returns a value you should cast to int *. (A pointer to an int.) As some have noted, typical practice in C is to let implicit casting take care of this. … Read more

Use of cudamalloc(). Why the double pointer?

All CUDA API functions return an error code (or cudaSuccess if no error occured). All other parameters are passed by reference. However, in plain C you cannot have references, that’s why you have to pass an address of the variable that you want the return information to be stored. Since you are returning a pointer, … Read more

Do I really need malloc?

TL;DR If you don’t know what you’re doing, use malloc or a fixed size array in all situations. VLA:s are not necessary at all. And do note that VLA:s cannot be static nor global. Do I really need to use malloc here? Yes. You’re reading a file. They are typically way bigger than what’s suitable … Read more