{"id":3435,"date":"2017-07-20T20:15:32","date_gmt":"2017-07-20T12:15:32","guid":{"rendered":"https:\/\/ixyzero.com\/blog\/?p=3435"},"modified":"2017-07-21T13:50:34","modified_gmt":"2017-07-21T05:50:34","slug":"linux%e4%b8%8b%e7%9a%84c%e8%af%ad%e8%a8%80%e5%ae%9e%e7%8e%b0%e5%87%bd%e6%95%b0%e5%8f%82%e6%95%b0%e4%b8%ad%e7%9a%84%e6%95%b0%e7%bb%84%e7%b1%bb%e5%9e%8b","status":"publish","type":"post","link":"https:\/\/ixyzero.com\/blog\/archives\/3435.html","title":{"rendered":"Linux\u4e0b\u7684C\u8bed\u8a00\u5b9e\u73b0#\u51fd\u6570\u53c2\u6570\u4e2d\u7684\u6570\u7ec4\u7c7b\u578b"},"content":{"rendered":"

=Start=<\/p>\n

\u7f18\u7531\uff1a<\/h4>\n

\u6807\u9898\u5176\u5b9e\u662f\u4e2a\u9519\u8bef\u7684\u8bf4\u6cd5\uff0c\u56e0\u4e3a\u5728C\u8bed\u8a00\u4e2d\u51fd\u6570\u53c2\u6570\u662f\u6ca1\u6709\u6570\u7ec4\u8fd9\u4e00\u7c7b\u578b\u7684<\/strong><\/span>\uff0c\u53ea\u662f\u6211\u4e4b\u524d\u8fd9\u4e48\u4ee5\u4e3a\u7684\u800c\u5df2\uff0c\u5728\u7a0b\u5e8f\u4e2d\u78b0\u5230\u7684\u4e00\u4e2a\u95ee\u9898\uff0c\u5728\u6b64\u8bb0\u5f55\u4e00\u4e0b\uff0c\u65b9\u4fbf\u4ee5\u540e\u53c2\u8003\u3002<\/p>\n

\u6b63\u6587\uff1a<\/h4>\n
\u53c2\u8003\u89e3\u7b54\uff1a<\/h5>\n

\u8d77\u56e0\u5728\u4e8e\u5982\u4e0b\u4e00\u6bb5\u4ee3\u7801\uff1a<\/p>\n

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int<\/code>\u00a0get_env_from_pid (<\/code>int<\/code>\u00a0pid,\u00a0<\/code>char<\/code>\u00a0environ[]) {<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>char<\/code>\u00a0file[PATH_MAX];<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>snprintf(file, PATH_MAX,\u00a0<\/code>\"\/proc\/%d\/environ\"<\/code>, pid);<\/code><\/div>\n
<\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>int<\/code>\u00a0i, r =\u00a0<\/code>0<\/code>, fd = open(file, O_RDONLY);<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>memset(environ,\u00a0<\/code>0<\/code>, ENV_LEN);<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>\/\/ printf(\"sizeof(environ) = %d\\n\", sizeof(environ));\u00a0\u00a0 \/\/ 8<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>\/\/ printf(\"sizeof(*environ) = %d\\n\", sizeof(*environ)); \/\/ 1<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>\/\/ printf(\"strlen(environ) = %d\\n\", strlen(environ));\u00a0\u00a0 \/\/ 0<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>if<\/code>\u00a0(fd >\u00a0<\/code>0<\/code>) {<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/code>\/\/ r = read(fd, environ, sizeof(environ)); \/\/ \u9519\u8bef\uff01<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/code>r = read(fd, environ, ENV_LEN);<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/code>close(fd);<\/code><\/div>\n
<\/div>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/code>for<\/code>\u00a0(i =\u00a0<\/code>0<\/code>; r >\u00a0<\/code>0<\/code>\u00a0&& i < r-<\/code>1<\/code>; i++) {<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/code>if<\/code>\u00a0(environ[i] ==\u00a0<\/code>0<\/code>)<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/code>environ[i] =\u00a0<\/code>'\\n'<\/code>;<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/code>}<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/code>return<\/code>\u00a00<\/code>;<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>}<\/code><\/div>\n
\u00a0\u00a0\u00a0\u00a0<\/code>return<\/code>\u00a0-<\/code>1<\/code>;<\/code><\/div>\n
}<\/code><\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n

Google\u4e86\u4e00\u4e0b\uff0c\u53d1\u73b0\u4e0b\u9762\u4e00\u6bb5\u89e3\u91ca\uff1a<\/p>\n

Function parameters never actually have array type.<\/strong><\/span> When the compiler sees<\/p>\n

void printarray(\u00a0double p[],\u00a0int s )<\/pre>\n
or even<\/p>\n
void printarray(\u00a0double p[100],\u00a0int s )<\/pre>\n
it converts either one to<\/p>\n
void printarray(\u00a0double* p,\u00a0int s )<\/pre>\n
So\u00a0sizeof(p)<\/code>\u00a0is\u00a0sizeof(double*)<\/code>. And yes, you’ll have to pass the size as a parameter.<\/p>\n
\u539f\u56e0\u5728\u4e8e\uff0cC\u8bed\u8a00\u4e0d\u662f\u4e00\u4e2a\u53cd\u5c04\u578b\u8bed\u8a00\uff0c\u5bf9\u8c61\u65e0\u6cd5\u81ea\u52a8\u77e5\u9053\u5b83\u662f\u4ec0\u4e48\u7c7b\u578b\u3001\u5927\u5c0f\u7b49\u4fe1\u606f\uff08C is not a reflective language. Objects don’t automatically know what they are.\uff09<\/p>\n
But you have many choices:<\/p>\n
    \n
  1. Obviously, add a parameter<\/li>\n
  2. Wrap the call in a macro and automatically add a parameter<\/li>\n
  3. Use a more complex object. Define a structure which contains the dynamic array and also the size of the array. Then, pass the address of the structure.<\/li>\n<\/ol>\n
    \u89e3\u51b3\u529e\u6cd5\u5728\u4e8e\uff1a<\/strong><\/p>\n
      \n
    1. \u4e3b\u52a8\u4f20\u4e00\u4e2a\u8868\u660e\u8be5\u6570\u7ec4\u5927\u5c0f\u7684\u53c2\u6570\uff1b<\/li>\n
    2. \u5c06\u8c03\u7528\u653e\u5728macro\u4e2d\uff08\u8ba9\u5b83\u81ea\u52a8\u5e2e\u4f60\u52a0\u4e00\u4e2a\u53c2\u6570\u4f20\u8fc7\u53bb\uff09\uff1b<\/li>\n
    3. \u4f7f\u7528\u4e00\u4e2a\u66f4\u590d\u6742\u7684\u5bf9\u8c61\/\u6570\u636e\u7ed3\u6784\uff0c\u5176\u4e2d\u5305\u542b\u4e86\u5b83\u7684\u5927\u5c0f\u7b49\u4fe1\u606f\uff1b<\/li>\n<\/ol>\n
      \u53c2\u8003\u94fe\u63a5\uff1a<\/h5>\n