fwrite writes size*nmemb bytes from memory to the current position of a stream. Its return value is the number of bytes written; a value below size*nmemb signals an error. section 14.4
Writing binary data
Open the stream in binary mode, call fwrite with a memory pointer, item size, item count, and stream, then check the returned byte count. A successful call advances the stream's file position by the bytes written. section 14.4
1 size_t fread(void* restrict ptr, size_t size, size_t nmemb,
2 FILE* restrict stream);
3 size_t fwrite(void const*restrict ptr, size_t size, size_t nmemb,
4 FILE* restrict stream);
5 int fseek(FILE* stream, long int offset, int whence);
6 long int ftell(FILE* stream);
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The related declarations show fwrite alongside fread, fseek, and ftell, clarifying its parameters and its role in positioned binary I/O. section 14.4
Use fwrite with these constraints:
- Use binary-mode streams for portable binary I/O; text-mode translation can alter a file's internal structure. section 14.4
- Combine fwrite with fseek and ftell to move through a file and write at selected positions. section 14.4
- Treat binary files as platform dependent, especially when preserving an object's internal representation. section 14.6
