gcc -o json-demo -g json-demo.c -std=c99 -I/usr/include/json -L/usr/lib/i386-linux-gnu/ -ljson

    1、json-demo和json-demo.c参数需要在前面，不能在后面，见错误1

    2、需要就爱如-std=c99,代码中需要，也可以用-std=gnu99，见错误2

    3、-I是json的头文件的路径

    4、-L是json库所在位置，这个路径可能根据系统不同而不同，建议用find / -name "libjson*"找到位置

    5、-ljson不可省略，尽量放在最后，没有这个参数会出现错误1的现象

jack@ubuntu:~/json-c$ gcc -I/usr/include/json -L/usr/lib/i386-linux-gnu/ -ljson -std=gnu99 -o json-demo -g json-demo.c 
/tmp/ccaITRtr.o: In function `GetValByKey‘: 
/home/jack/json-c/json-demo.c:13: undefined reference to `json_object_object_get‘ 
/home/jack/json-c/json-demo.c:16: undefined reference to `json_object_get_type‘ 
/home/jack/json-c/json-demo.c:20: undefined reference to `json_object_get_string‘ 
/home/jack/json-c/json-demo.c:23: undefined reference to `json_object_get_int‘ 
/tmp/ccaITRtr.o: In function `main‘: 
/home/jack/json-c/json-demo.c:39: undefined reference to `json_object_new_string‘ 
/home/jack/json-c/json-demo.c:41: undefined reference to `json_object_get_string‘ 
/home/jack/json-c/json-demo.c:43: undefined reference to `json_object_to_json_string‘ 
******

jack@ubuntu:~/json-c$ gcc -o json-demo -g json-demo.c -I/usr/include/json -L/usr/lib/i386-linux-gnu/ -ljson 
json-demo.c: In function ‘main’: 
json-demo.c:87:2: error: ‘for’ loop initial declarations are only allowed in C99 mode 
json-demo.c:87:2: note: use option -std=c99 or -std=gnu99 to compile your code