由于历史原因，以及不同开发人员的技术偏好，C语言和C++语言都有一些独有的非常有价值的项目，因而两种语言的互操作，充分利用前人造的轮子是一件非常有价值的事情。
C++代码调用C代码很简单，只要分别在包含的C头文件的开头和结尾加上如下的两个块：
#ifdef __cplusplus
extern "C" {
#endif
和
#ifdef __cplusplus
}
#endif
即可。
然而为了支持类、重载等更加高级的特性，在编译C++代码时，C++符号会被修饰。我们dump Linux平台加密库 libcrypto++ 的符号表，可以看到如下的内容：
$ readelf -s /usr/lib/libcrypto++.so
Symbol table '.dynsym' contains 9607 entries:
Num: Value Size Type Bind Vis Ndx Name
0: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND
1: 00000000001daa58 0 SECTION LOCAL DEFAULT 9
2: 0000000000000000 0 OBJECT GLOBAL DEFAULT UND _ZTIi@CXXABI_1.3 (2)
3: 0000000000000000 0 FUNC GLOBAL DEFAULT UND __errno_location@GLIBC_2.2.5 (3)
4: 0000000000000000 0 FUNC GLOBAL DEFAULT UND _ZSt18uncaught_exceptionv@GLIBCXX_3.4 (4)
5: 0000000000000000 0 FUNC GLOBAL DEFAULT UND _ZNSt8__detail15_List_node_base7_M_hookEPS0_@GLIBCXX_3.4.15 (5)
6: 0000000000000000 0 FUNC GLOBAL DEFAULT UND getservbyname@GLIBC_2.2.5 (6)
7: 0000000000000000 0 FUNC GLOBAL DEFAULT UND bind@GLIBC_2.2.5 (6)
8: 0000000000000000 0 FUNC GLOBAL DEFAULT UND _ZSt29_Rb_tree_insert_and_rebalancebPSt18_Rb_tree_node_baseS0_RS_@GLIBCXX_3.4 (4)
9: 0000000000000000 0 FUNC GLOBAL DEFAULT UND __longjmp_chk@GLIBC_2.11 (7)
10: 0000000000000000 0 OBJECT GLOBAL DEFAULT UND _ZTIh@CXXABI_1.3 (2)
11: 0000000000000000 0 OBJECT GLOBAL DEFAULT UND _ZTVSt9basic_iosIcSt11char_traitsIcEE@GLIBCXX_3.4 (4)
12: 0000000000000000 0 FUNC GLOBAL DEFAULT UND socket@GLIBC_2.2.5 (6)
13: 0000000000000000 0 FUNC GLOBAL DEFAULT UND _ZNSt14basic_ifstreamIcSt11char_traitsIcEED1Ev@GLIBCXX_3.4 (4)
. . . . . .
86: 0000000000000000 0 FUNC GLOBAL DEFAULT UND _ZNSo5writeEPKcl@GLIBCXX_3.4 (4)
87: 0000000000000000 0 FUNC GLOBAL DEFAULT UND malloc@GLIBC_2.2.5 (6)
88: 0000000000000000 0 FUNC GLOBAL DEFAULT UND _ZNSt9basic_iosIcSt11char_traitsIcEE4initEPSt15basic_streambufIcS1_E@GLIBCXX_3.4 (4)
89: 0000000000000000 0 FUNC GLOBAL DEFAULT UND _ZNSi5seekgElSt12_Ios_Seekdir@GLIBCXX_3.4 (4)
90: 0000000000000000 0 FUNC GLOBAL DEFAULT UND pthread_key_delete@GLIBC_2.2.5 (3)
91: 0000000000000000 0 FUNC GLOBAL DEFAULT UND shutdown@GLIBC_2.2.5 (6)
92: 0000000000000000 0 FUNC GLOBAL DEFAULT UND _ZSt15set_new_handlerPFvvE@GLIBCXX_3.4 (4)
93: 0000000000000000 0 FUNC GLOBAL DEFAULT UND pthread_getspecific@GLIBC_2.2.5 (3)
94: 0000000000000000 0 FUNC GLOBAL DEFAULT UND strcmp@GLIBC_2.2.5 (6)
95: 0000000000000000 0 FUNC GLOBAL DEFAULT UND strtol@GLIBC_2.2.5 (6)
96: 0000000000000000 0 FUNC GLOBAL DEFAULT UND ioctl@GLIBC_2.2.5 (6)
. . . . . .
186: 00000000002c5a80 142 FUNC GLOBAL DEFAULT 12 _ZN8CryptoPP6xorbufEPhPKhS2_m
187: 00000000002fd6d0 9 FUNC WEAK DEFAULT 12 _ZN8CryptoPP21InvertibleRSAFunction9BERDecodeERNS_22BufferedTransformationE
188: 00000000001ea840 73 FUNC GLOBAL DEFAULT 12 _ZN8CryptoPP13Base64Decoder22GetDecodingLookupArrayEv
189: 0000000000249760 6 FUNC WEAK DEFAULT 12 _ZThn8_N8CryptoPP13DL_SignerImplINS_25DL_SignatureSchemeOptionsINS_5DL_SSINS_13DL_Keys_ECDSAINS_4EC2NEEENS_18DL_Algorithm_ECDSAIS4_EENS_37DL_SignatureMessageEncodingMethod_DSAENS_6SHA256EiEES5_S7_S8_S9_EEED0Ev
190: 0000000000278b60 86 FUNC WEAK DEFAULT 12 _ZN8CryptoPP8Rijndael3DecD1Ev
191: 00000000001fd1f0 2 FUNC WEAK DEFAULT 12 _ZN8CryptoPP23DefaultEncryptorWithMAC8FirstPutEPKh
192: 000000000026a490 51 FUNC GLOBAL DEFAULT 12 _ZN8CryptoPP23FilterWithBufferedInputC2EPNS_22BufferedTransformationE
193: 0000000000285180 6 FUNC WEAK DEFAULT 12 _ZNK8CryptoPP8GCM_Base6IVSizeEv
194: 000000000032e830 510 FUNC WEAK DEFAULT 12 _ZN8CryptoPP18StandardReallocateItNS_20AllocatorWithCleanupItLb0EEEEENT0_7pointerERS3_PT_NS3_9size_typeES8_b
195: 00000000002a1790 185 FUNC WEAK DEFAULT 12 _ZSt18uninitialized_copyISt15_Deque_iteratorIyRKyPS1_ES0_IyRyPyEET0_T_S9_S8_
196: 0000000000355610 25 OBJECT WEAK DEFAULT 14 _ZTSN8CryptoPP11RSAFunctionE
. . . . . .
