Create a tensor file in C [OpenCV]

Hi, I should create a txt file that represent a tensor in Torch... This is my problem: In a .c file (but I can also use C++ language and I don't know how it is possible...) I have to create a file that can be read in another file .lua with torch.load() function... My problem is that: how can I write the byte of an image in a txt file? Thanks in advance.