无法使用 g++ 进行编译

Question

现在我尝试使用一个名为“GAUL”的开源工具，其中实现了一些遗传算法。通过编译示例文件，我发现我只能通过使用 gcc 而不是 g++ 来编译这些数据。例如：

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1) 使用gcc -I /usr/local/include/ -c wildfire_threat.c -o test.o

gcc** -g -O2 -Wall -o test2.out test.o -lgaul -lgaul_util -lm -lpthread -lslang -lm

也适用于组合

gcc -I /usr/local/include/ -c wildfire_threat.c -o test.o

g++ -g -O2 -Wall -o test2.out test.o -lgaul -lgaul_util -lm -lpthread -lslang -lm

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但是 2) 使用

g++ -I /usr/local/include/ -c wildfire_threat.c -o test.o

g++ -g -O2 -Wall -o test2.out test.o -lgaul -lgaul_util -lm -lpthread -lslang -lm

我收到以下错误消息：

test.o: In function `wildfire_simulation(int*, bool)':
wildfire_threat.c:(.text+0x52): undefined reference to `random_int(unsigned int)'
wildfire_threat.c:(.text+0x74): undefined reference to `random_int(unsigned int)'
test.o: In function `wildfire_score(population_t*, entity_t*)':
wildfire_threat.c:(.text+0xb55): undefined reference to `ga_entity_set_fitness(entity_t*, double)'
test.o: In function `wildfire_seed(population_t*, entity_t*)':
wildfire_threat.c:(.text+0xb86): undefined reference to `random_boolean()'
wildfire_threat.c:(.text+0xbb9): undefined reference to `random_boolean_prob(double)'
wildfire_threat.c:(.text+0xc18): undefined reference to `random_int(unsigned int)'
wildfire_threat.c:(.text+0xc25): undefined reference to `random_int(unsigned int)'
wildfire_threat.c:(.text+0xc92): undefined reference to `random_int(unsigned int)'
test.o: In function `wildfire_mutate_flip(population_t*, entity_t*, entity_t*)': 
wildfire_threat.c:(.text+0xd41): undefined reference to `random_int(unsigned int)'
test.o: In function `wildfire_crossover(population_t*, entity_t*, entity_t*, entity_t*, entity_t*)':
wildfire_threat.c:(.text+0xe25): undefined reference to `random_boolean()' 
wildfire_threat.c:(.text+0xe37): undefined reference to `random_int(unsigned int)' 
wildfire_threat.c:(.text+0xff0): undefined reference to `random_int(unsigned int)'
test.o: In function `wildfire_ga_callback(int, population_t*)':
wildfire_threat.c:(.text+0x11bc): undefined reference to `ga_get_entity_from_rank(population_t*, unsigned int)'
wildfire_threat.c:(.text+0x11c4): undefined reference to `ga_entity_get_fitness(entity_t*)'
wildfire_threat.c:(.text+0x11ef): undefined reference to 
`ga_population_score_and_sort(population_t*)' 
wildfire_threat.c:(.text+0x1206): undefined reference to `ga_fitness_mean_stddev(population_t*, double*, double*)'
wildfire_threat.c:(.text+0x122b): undefined reference to `ga_get_entity_from_rank(population_t*, unsigned int)'
wildfire_threat.c:(.text+0x1233): undefined reference to `ga_entity_get_fitness(entity_t*)'
wildfire_threat.c:(.text+0x1268): undefined reference to `ga_get_entity_from_rank(population_t*, unsigned int)'
wildfire_threat.c:(.text+0x1270): undefined reference to `ga_entity_get_fitness(entity_t*)'
test.o: In function `main':
wildfire_threat.c:(.text+0x12b0): undefined reference to `random_seed(unsigned int)'
wildfire_threat.c:(.text+0x12dd): undefined reference to `ga_select_two_roulette_rebased(population_t*, entity_t**, entity_t**)'
wildfire_threat.c:(.text+0x12e6): undefined reference to `ga_select_one_roulette_rebased(population_t*, entity_t**)'
wildfire_threat.c:(.text+0x132e): undefined reference to `ga_genesis_integer(int, int, int, bool (*)(int, population_t*), bool (*)(int, entity_t*), void (*)(void*), void (*)(void*), bool (*)(population_t*, entity_t*), bool (*)(population_t*, entity_t*), entity_t* (*)(population_t*, entity_t*), bool (*)(population_t*, entity_t**), bool (*)(population_t*, entity_t**, entity_t**), void (*)(population_t*, entity_t*, entity_t*), void (*)(population_t*, entity_t*, entity_t*, entity_t*, entity_t*), void (*)(population_t*, entity_t*), void*)'
wildfire_threat.c:(.text+0x135c): undefined reference to `ga_population_set_parameters(population_t*, ga_scheme_type_t, ga_elitism_type_t, double, double, double)'
wildfire_threat.c:(.text+0x136d): undefined reference to `ga_evolution_threaded(population_t*, int)'
wildfire_threat.c:(.text+0x137e): undefined reference to `ga_get_entity_from_rank(population_t*, unsigned int)'
wildfire_threat.c:(.text+0x1386): undefined reference to `ga_entity_get_fitness(entity_t*)'
wildfire_threat.c:(.text+0x13b5): undefined reference to `ga_get_entity_from_rank(population_t*, unsigned int)'
wildfire_threat.c:(.text+0x1434): undefined reference to `ga_get_entity_from_rank(population_t*, unsigned int)'
wildfire_threat.c:(.text+0x1528): undefined reference to `ga_extinction(population_t*)'
collect2: ld returned 1 exit status

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谁能向我解释这个谜，以及我如何避免使用 gcc，因为这会给我想要嵌入的剩余源代码带来问题？

Answer 1

您应该使用 C 编译器编译 C 源代码，并使用 C++ 编译器编译 C++ 源代码。在特定情况下，GAUL 库是用 C 编写的，它的头文件不适合包含在 C++ 编译中 - 它们缺少 extern "C"，因此当您编译为 C++ 时，函数使用 C++ 链接声明，当然，不能可以在 C 编译的库中找到。

Answer 2

您的第三方 C 库可能在其标头中缺少 extern "C" 声明。要在不修改第三方标头的情况下解决此问题，您可以在您的 C++ 源代码中执行类似的操作 #include 相关的第三方标头：

extern "C" {
  #include "gaul.h"         // note: I'm just guessing the names of the
  #include "gaul_utils.h"   //       actual header files here...
}