1.有关#define与#ifdef的问题

whitetiger8 2002-04-21 06:46:12

大家看代码：
#ifndef dllmainh
#define dllmainh
....
#endif
....
请问第一句与第二句的意思是什么呢？主要是第二句，它定义的是谁啊？虽然它目的是声明一个特定的字符串，可是它代表谁呢？怎么看？

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jerrymousenet2 2002-04-21

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老兄多看看帮助吧！

jerrymousenet2 2002-04-21

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又是你。

whitetiger8 2002-04-21

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谢谢！

jishiping 2002-04-21

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这样做的目的是不让头文件重复定义。这儿的名字并不一定非要是dllmainh，
只要在你的程序中不要重复定义就可以了。一般来说，名字取为头文件的文件
名，将文件名的.去掉，这样就肯定不会重复了。

最近在看Linux底层代码，发现好多代码里有#define #ifdef #endif，找了个介绍详细的文章，供大家参考！

8192CU LINUX驱动/****************************************************************************** * * Copyright(c) 2007 - 2011 Realtek Corporation. All rights reserved. * * This program is free software; you can redistribute it and/or modify it * under the terms of version 2 of the GNU General Public License as * published by the Free Software Foundation. * * This program is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for * more details. * * You should have received a copy of the GNU General Public License along with * this program; if not, write to the Free Software Foundation, Inc., * 51 Franklin Street, Fifth Floor, Boston, MA 02110, USA * * ******************************************************************************/ /* * Public General Config */ #define AUTOCONF_INCLUDED #define RTL871X_MODULE_NAME "92CU" #define DRV_NAME "rtl8192cu" #define CONFIG_USB_HCI 1 #define CONFIG_RTL8192C 1 #define PLATFORM_LINUX 1 //#define CONFIG_IOCTL_CFG80211 1 #ifdef CONFIG_IOCTL_CFG80211 #define CONFIG_CFG80211_FORCE_COMPATIBLE_2_6_37_UNDER //#define CONFIG_DEBUG_CFG80211 1 #endif /* * Internal General Config */ //#define CONFIG_PWRCTRL //#define CONFIG_H2CLBK #define CONFIG_EMBEDDED_FWIMG 1 //#define CONFIG_FILE_FWIMG #ifdef CONFIG_WAKE_ON_WLAN #define CONFIG_WOWLAN 1 #endif //CONFIG_WAKE_ON_WLAN #define CONFIG_R871X_TEST 1 #define CONFIG_80211N_HT 1 #define CONFIG_RECV_REORDERING_CTRL 1 //#define CONFIG_TCP_CSUM_OFFLOAD_RX 1 //#define CONFIG_DRVEXT_MODULE 1 #ifndef CONFIG_MP_INCLUDED #define CONFIG_IPS 1 #ifdef CONFIG_IPS //#define CONFIG_IPS_LEVEL_2 1 //enable this to set default IPS mode to IPS_LEVEL_2 #endif #define SUPPORT_HW_RFOFF_DETECTED 1 #define CONFIG_LPS 1 #define CONFIG_BT_COEXIST 1 //befor link #define CONFIG_ANTENNA_DIVERSITY //after link #ifdef CONFIG_ANTENNA_DIVERSITY #define CONFIG_SW_ANTENNA_DIVERSITY //#define CONFIG_HW_ANTENNA_DIVERSITY #endif #define CONFIG_IOL #else //#ifndef CONFIG_MP_INCLUDED #define CONFIG_MP_IWPRIV_SUPPORT 1 #endif //#ifndef CONFIG_MP_INCLUDED #define CONFIG_AP_MODE 1 #define CONFIG_NATIVEAP_MLME 1 // Added by Albert 20110314 #define CONFIG_P2P 1 #ifdef CONFIG_P2P // Added by Albert 20110812 // The CONFIG_WFD is for supporting the Wi-Fi display //#define CONFIG_WFD 1 // Unmarked if there is low p2p scanned ratio; Kurt //#define CONFIG_P2P_AGAINST_NOISE 1 #define CONFIG_P2P_REMOVE_GROUP_INFO //#define CONFIG_DBG_P2P #endif // Added by Kurt 20110511 //#define CONFIG_TDLS 1 #ifdef CONFIG_TDLS #define CONFIG_TDLS_AUTOSETUP 1 #define CONFIG_TDLS_AUTOCHECKALIVE 1 #endif #ifdef CONFIG_AP_MODE #ifndef CONFIG_NATIVEAP_MLME #define CONFIG_HOSTAPD_MLME 1 #endif #define CONFIG_FIND_BEST_CHANNEL 1 #endif #define CONFIG_SKB_COPY 1//for amsdu #define CONFIG_LED #ifdef CONFIG_LED #define CONFIG_SW_LED #ifdef CONFIG_SW_LED //#define CONFIG_LED_HANDLED_BY_CMD_THREAD #endif #endif // CONFIG_LED #define USB_INTERFERENCE_ISSUE // this should be checked in all usb interface #define CONFIG_GLOBAL_UI_PID #define CONFIG_LAYER2_ROAMING #define CONFIG_LAYER2_ROAMING_RESUME //#define CONFIG_ADAPTOR_INFO_CACHING_FILE // now just applied on 8192cu only, should make it general... //#define CONFIG_RESUME_IN_WORKQUEUE //#define CONFIG_SET_SCAN_DENY_TIMER #define CONFIG_LONG_DELAY_ISSUE #define CONFIG_NEW_SIGNAL_STAT_PROCESS //#define CONFIG_SIGNAL_DISPLAY_DBM //display RX signal with dbm #ifdef CONFIG_IOL #define CONFIG_IOL_LLT #define CONFIG_IOL_MAC #define CONFIG_IOL_BB_PHY_REG #define CONFIG_IOL_BB_AGC_TAB #define CONFIG_IOL_RF_RF90_PATH_A #define CONFIG_IOL_RF_RF90_PATH_B #endif #define CONFIG_BR_EXT 1 // Enable NAT2.5 support for STA mode interface with a L2 Bridge #ifdef CONFIG_BR_EXT #define CONFIG_BR_EXT_BRNAME "br0" #endif // CONFIG_BR_EXT #define CONFIG_TX_MCAST2UNI 1 // Support IP multicast->unicast //#define CONFIG_CHECK_AC_LIFETIME 1 // Check packet lifetime of 4 ACs. /* * Interface Related Config */ //#define CONFIG_USB_INTERRUPT_IN_PIPE 1 #ifndef CONFIG_MINIMAL_MEMORY_USAGE #define CONFIG_USB_TX_AGGREGATION 1 #define CONFIG_USB_RX_AGGREGATION 1 #endif #define CONFIG_PREALLOC_RECV_SKB 1 //#define CONFIG_REDUCE_USB_TX_INT 1 // Trade-off: Improve performance, but may cause TX URBs blocked by USB Host/Bus driver on few platforms. //#define CONFIG_EASY_REPLACEMENT 1 /* * CONFIG_USE_USB_BUFFER_ALLOC_XX uses Linux USB Buffer alloc API and is for Linux platform only now! */ #define CONFIG_USE_USB_BUFFER_ALLOC_TX 1 // Trade-off: For TX path, improve stability on some platforms, but may cause performance degrade on other platforms. //#define CONFIG_USE_USB_BUFFER_ALLOC_RX 1 // For RX path /* * USB VENDOR REQ BUFFER ALLOCATION METHOD * if not set we'll use function local variable (stack memory) */ //#define CONFIG_USB_VENDOR_REQ_BUFFER_DYNAMIC_ALLOCATE #define CONFIG_USB_VENDOR_REQ_BUFFER_PREALLOC #define CONFIG_USB_VENDOR_REQ_MUTEX #define CONFIG_VENDOR_REQ_RETRY //#define CONFIG_USB_SUPPORT_ASYNC_VDN_REQ 1 /* * HAL Related Config */ #define RTL8192C_RX_PACKET_NO_INCLUDE_CRC 1 #define SUPPORTED_BLOCK_IO #define RTL8192CU_FW_DOWNLOAD_ENABLE 1 #define CONFIG_ONLY_ONE_OUT_EP_TO_LOW 0 #define CONFIG_OUT_EP_WIFI_MODE 0 #define ENABLE_USB_DROP_INCORRECT_OUT 0 #define RTL8192CU_ASIC_VERIFICATION 0 // For ASIC verification. #define RTL8192CU_ADHOC_WORKAROUND_SETTING 1 #define DISABLE_BB_RF 0 #define RTL8191C_FPGA_NETWORKTYPE_ADHOC 0 #ifdef CONFIG_MP_INCLUDED #define MP_DRIVER 1 #undef CONFIG_USB_TX_AGGREGATION #undef CONFIG_USB_RX_AGGREGATION #else #define MP_DRIVER 0 #endif /* * Platform Related Config */ #ifdef CONFIG_PLATFORM_MN10300 #define CONFIG_SPECIAL_SETTING_FOR_FUNAI_TV #if defined (CONFIG_SW_ANTENNA_DIVERSITY) #undef CONFIG_SW_ANTENNA_DIVERSITY #define CONFIG_HW_ANTENNA_DIVERSITY #endif #endif #ifdef CONFIG_WISTRON_PLATFORM #endif #ifdef CONFIG_PLATFORM_TI_DM365 #define CONFIG_USE_USB_BUFFER_ALLOC_RX 1 #endif /* * Debug Related Config */ //#define CONFIG_DEBUG_RTL871X #define DBG 0 #define CONFIG_DEBUG_RTL819X #define CONFIG_PROC_DEBUG 1 //#define DBG_IO //#define DBG_DELAY_OS //#define DBG_MEM_ALLOC //#define DBG_IOCTL //#define DBG_TX //#define DBG_XMIT_BUF //#define DBG_TX_DROP_FRAME //#define DBG_RX_DROP_FRAME //#define DBG_RX_SEQ //#define DBG_RX_SIGNAL_DISPLAY_PROCESSING //#define DBG_RX_SIGNAL_DISPLAY_SSID_MONITORED "jeff-ap" //#define DBG_EXPIRATION_CHK //#define DBG_SHOW_MCUFWDL_BEFORE_51_ENABLE //#define DBG_ROAMING_TEST //#define DBG_HAL_INIT_PROFILING #define DBG_MEMORY_LEAK 1 #define DBG_CONFIG_ERROR_DETECT //#define DBG_CONFIG_ERROR_RESET

参考链接: GLSL_ES_Specification_3.00 预处理 #version #version 300 es //定义glsl版本 #if #define #undef #if #ifdef #ifndef #else #elif #endif #define USE_LIGHT #define LIGHT_NUMBER 10 ... #ifdef USE_LIGHT .... #else ... #endif #error #pragma #pragma STDGL invariant(all) //保证所有输出变量必须精确一致 //但会降低optimize效率，降低性

之前没有写过什么大工程，所以没有怎么关注过条件编译。今天在看代码的时候发现里面用到了#define和#ifdef来调试代码。于是就看了一下。顺便再做个笔记。先介绍一下条件编译：条件编译是根据实际定义的宏（可以认为是某一类条件）进行代码静态编译的手段。可以根据表达式的值或者某个特定宏是否被定义来确定编译条件。在看几个预编译指令（预编译指令很多，这次只介绍用到的三个）： #...

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