c - 分割字符串而不影响源

Question

如何strtok 文件名以使原始字符串不会受到影响？

void generate_header(int sock, char* filename, int response_code) {

  char buffer[BUFLEN];

  // For Content-Type generation                                                                                                   
  char *file_format;
  const char delimiter[2] = ".";
  file_format = strtok(filename, delimiter);
  file_format = strtok(NULL, delimiter);

  // Generate response code                                                                                                        
  /*
  ........ ommited ..........
  */

  // Generate Content-Type                                                                                                         
  if (strcmp(file_format, "html") == 0 || strcmp(file_format, "htm") == 0) {
    strncat(buffer, "Content-Type: text/html\n", sizeof(buffer) - strlen(buffer) - 1);
  }
  else if (strcmp(file_format, "txt") == 0) {
    strncat(buffer, "Content-Type: text/plain\n", sizeof(buffer) - strlen(buffer) - 1);
  }
  else if (strcmp(file_format, "jpg") == 0 || strcmp(file_format, "jpeg") == 0) {
    strncat(buffer, "Content-Type: image/jpeg\n", sizeof(buffer) - strlen(buffer) - 1);
  }
  else if (strcmp(file_format, "gif") == 0) {
    strncat(buffer, "Content-Type: image/gif\n", sizeof(buffer) - strlen(buffer) - 1);
  } else {
    strncat(buffer, "Content-Type: application/octet-stream\n", sizeof(buffer) - strlen(buffer) - 1);
  }

  // End                                                                                                                           
  strncat(buffer, "Connection: close\n", sizeof(buffer) - strlen(buffer) - 1);

  // Push                                                                                                                          
  write(sock, buffer, strlen(buffer));
}

Answer 1

你不需要strtok，strrchr可以找到最后一次出现的分隔符:

if((file_format = strrchr(filename, '.')) == NULL)
    file_format = ""; /* no delimiter present */
else
    ++file_format; /* step over the delimiter */