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stringsNull-terminated wide stringsstrcatstrcat_sstrchrstrcmpstrcollstrcpystrcpy_sstrcspnstrerrorstrerrorlen_sstrerror_sStrings librarystrlenstrncatThread supportcall_oncecnd_broadcastcnd_destroycnd_initcnd_signalcnd_timedwaitcnd_waitmtx_destroymtx_initmtx_lockmtx_plainmtx_recursivemtx_timedmtx_timedlockmtx_trylockmtx_unlockonce_flagONCE_FLAG_INITthrd_busythrd_createthrd_currentthrd_detachthrd_equalthrd_errorthrd_exitthrd_jointhrd_nomemthrd_sleepthrd_successthrd_timedoutthrd_yieldThread support librarythread_localtss_createtss_deleteTSS_DTOR_ITERATIONStss_gettss_setType supportBoolean type support libraryFixed width integer typesFLT_EVAL_METHODFLT_ROUNDSmax_align_tNULLNumeric limitsoffsetofptrdiff_tsize_tType supportVariadic functionsVariadic functionsva_argva_copyva_endva_listva_start

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在头文件<stdarg.h>中定义



void va_copy（va_list dest，va_list src）;


（自C99以来）

va_copy宏将src复制到dest。

va_end应在函数返回之前在dest上调用，或者任何后续的dest重新初始化（通过调用va_start或va_copy）。

参数

dest

-

一个要初始化的va_list类型的实例

SRC

-

将用于初始化dest的源va_list

扩大价值

(none).

例

#include <stdio.h>#include <stdarg.h>#include <math.h>
 double sample_stddev(int count, ...) {    /* Compute the mean with args1. */
    double sum = 0;
    va_list args1;    va_start(args1, count);
    va_list args2;    va_copy(args2, args1);   /* copy va_list object */    for (int i = 0; i < count; ++i) {
        double num = va_arg(args1, double);
        sum += num;    }    va_end(args1);
    double mean = sum / count; 
    /* Compute standard deviation with args2 and mean. */
    double sum_sq_diff = 0;    for (int i = 0; i < count; ++i) {
        double num = va_arg(args2, double);
        sum_sq_diff += (num-mean) * (num-mean);    }    va_end(args2);    return sqrt(sum_sq_diff / count);}
 int main(void) {    printf("%f\n", sample_stddev(4, 25.0, 27.3, 26.9, 25.7));}

可能的输出：

0.920258

参考

  • C11标准（ISO / IEC 9899：2011）：

    • 7.16.1.2 va_copy宏（p：270）

  • C99标准（ISO / IEC 9899：1999）：

    • 7.15.1.2 va_copy宏（p：250）

扩展内容

va_arg

访问下一个可变参数函数参数（函数宏）

va_end

结束可变参数函数参数的遍历（函数宏）

va_list

保存va_start，va_arg，va_end和va_copy（typedef）所需的信息

va_start

允许访问可变参数函数参数（函数宏）

| 用于va_copy的C ++文档 |

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