警告：初始化元素在加载时不可计算
warning: initializer element is not computable at load time
我无法理解 gcc -pedantic 在以下情况下的输出：
$ gcc -pedantic parse.c -lpopt
parse.c: In function ‘main’:
parse.c:19:7: warning: initializer element is not computable at load time
{ "bps", 'b', POPT_ARG_INT, &speed, 0,
^
parse.c:20:7: warning: initializer element is not computable at load time
"signaling rate in bits-per-second", "BPS" },
^
parse.c:27:7: warning: initializer element is not computable at load time
{ "raw", 'r', 0, &raw, 0,
^
parse.c:28:7: warning: initializer element is not computable at load time
"don't perform any character conversions" },
^
使用以下 C 代码（取自 here）：
$ cat parse.c
#include <popt.h>
int main(int argc, const char *argv[]) {
char c; /* used for argument parsing */
int speed = 0; /* used in argument parsing to set speed */
int raw = 0; /* raw mode? */
struct poptOption optionsTable[] = {
{ "bps", 'b', POPT_ARG_INT, &speed, 0,
"signaling rate in bits-per-second", "BPS" },
{ "crnl", 'c', 0, 0, 'c',
"expand cr characters to cr/lf sequences" },
{ "hwflow", 'h', 0, 0, 'h',
"use hardware (RTS/CTS) flow control" },
{ "noflow", 'n', 0, 0, 'n',
"use no flow control" },
{ "raw", 'r', 0, &raw, 0,
"don't perform any character conversions" },
{ "swflow", 's', 0, 0, 's',
"use software (XON/XOF) flow control" } ,
POPT_AUTOHELP
{ NULL, 0, 0, NULL, 0 }
};
}
使用 -ansi 或 -std=c89 可以编译完全相同的代码。为什么 -pedantic 选项失败了？
使用：
$ gcc --version
gcc (Debian 4.9.1-19) 4.9.1
Copyright (C) 2014 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
和
$ apt-cache policy libpopt-dev
libpopt-dev:
Installed: 1.16-10
Candidate: 1.16-10
Version table:
*** 1.16-10 0
500 http://ftp.fr.debian.org/debian/ jessie/main amd64 Packages
100 /var/lib/dpkg/status
在C89标准中，初始化列表必须是编译时常量表达式，因此会出现警告。但是在 C99 中它是受支持的。
在C89中，您可以：
struct poptOption optionsTable[2];
optionsTable[0] = {"bps", 'b', POPT_ARG_INT, &speed, 0,
"signaling rate in bits-per-second", "BPS" };
optionsTable[1] = {"crnl", 'c', 0, 0, 'c',
"expand cr characters to cr/lf sequences" };
因为变量速度是在栈上分配的，它的地址在编译时是未知的。只有当 main() 正在执行时，它的地址才会被知道。变量 raw 也一样。与任何优秀的编译器一样，您的编译器的错误消息不会准确指向错误的元素，并且让您头疼地理解它在抱怨什么。
我无法理解 gcc -pedantic 在以下情况下的输出：
$ gcc -pedantic parse.c -lpopt
parse.c: In function ‘main’:
parse.c:19:7: warning: initializer element is not computable at load time
{ "bps", 'b', POPT_ARG_INT, &speed, 0,
^
parse.c:20:7: warning: initializer element is not computable at load time
"signaling rate in bits-per-second", "BPS" },
^
parse.c:27:7: warning: initializer element is not computable at load time
{ "raw", 'r', 0, &raw, 0,
^
parse.c:28:7: warning: initializer element is not computable at load time
"don't perform any character conversions" },
^
使用以下 C 代码（取自 here）：
$ cat parse.c
#include <popt.h>
int main(int argc, const char *argv[]) {
char c; /* used for argument parsing */
int speed = 0; /* used in argument parsing to set speed */
int raw = 0; /* raw mode? */
struct poptOption optionsTable[] = {
{ "bps", 'b', POPT_ARG_INT, &speed, 0,
"signaling rate in bits-per-second", "BPS" },
{ "crnl", 'c', 0, 0, 'c',
"expand cr characters to cr/lf sequences" },
{ "hwflow", 'h', 0, 0, 'h',
"use hardware (RTS/CTS) flow control" },
{ "noflow", 'n', 0, 0, 'n',
"use no flow control" },
{ "raw", 'r', 0, &raw, 0,
"don't perform any character conversions" },
{ "swflow", 's', 0, 0, 's',
"use software (XON/XOF) flow control" } ,
POPT_AUTOHELP
{ NULL, 0, 0, NULL, 0 }
};
}
使用 -ansi 或 -std=c89 可以编译完全相同的代码。为什么 -pedantic 选项失败了？
使用：
$ gcc --version
gcc (Debian 4.9.1-19) 4.9.1
Copyright (C) 2014 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
和
$ apt-cache policy libpopt-dev
libpopt-dev:
Installed: 1.16-10
Candidate: 1.16-10
Version table:
*** 1.16-10 0
500 http://ftp.fr.debian.org/debian/ jessie/main amd64 Packages
100 /var/lib/dpkg/status
在C89标准中，初始化列表必须是编译时常量表达式，因此会出现警告。但是在 C99 中它是受支持的。
在C89中，您可以：
struct poptOption optionsTable[2];
optionsTable[0] = {"bps", 'b', POPT_ARG_INT, &speed, 0,
"signaling rate in bits-per-second", "BPS" };
optionsTable[1] = {"crnl", 'c', 0, 0, 'c',
"expand cr characters to cr/lf sequences" };
因为变量速度是在栈上分配的，它的地址在编译时是未知的。只有当 main() 正在执行时，它的地址才会被知道。变量 raw 也一样。与任何优秀的编译器一样，您的编译器的错误消息不会准确指向错误的元素，并且让您头疼地理解它在抱怨什么。