C++ Fprintf正在写入多个 struct 成员，并且数据过剩

当程序写入选定的文件(暂时覆盖它)时，它还会写入 struct 中的下一个成员

#include <stdio.h>
#include <string.h>
#include <sodium.h>
#include <tomcrypt.h>
struct user {
  char uName[32];
  char salt[16];
  char hash[32];
};
int main(int argc, char **argv){
  if (sodium_init() < 0) {
      return 1;
  }
  if(argc != 4){puts("Invalid number of arguments"); return 0;}
  struct user users[1];
  char passSalt[32 + 16];
  char hash[32];
  char salt[16];
  for(int i = 0; i < 16; i++){
    salt[i] = randombytes_uniform(127);
  }
  strcpy(passSalt, argv[3]);
  strncpy(passSalt, salt, 16);
  hash_state md;
  sha256_init(&md);
  sha256_process(&md, passSalt, 16);
  sha256_done(&md, hash);
  strncpy(users[0].uName, argv[2], 32);
  strncpy(users[0].hash, hash, 32);
  strncpy(users[0].salt, salt, 16);
  FILE *fp = fopen(argv[1], "w+");
  fprintf(fp, "%s %s %s\n", users[0].uName, users[0].hash, users[0].salt);
  fclose(fp);
}

Arguments used: ./write db abc qwertyuiop What is written to file: abc [ôÓBmdÂûÆ_LÂ¥ïÖ]lG31GfPmŽ@ÙûªŒU to~497s\0JmA[ôÓBmdÂûÆ_LÂ¥ïÖ]lG31GfPmŽ@ÙûªŒU

[ôÓBmdÂûÆ_LÂ¥ïÖ]lG31GfPmŽ@ÙûªŒU is written twice and @ÙûªŒU should not be written at all because the hash is only 32 bytes long