将字符串转换为数字

下列函数可以将字符串转换为数字：

函数名 作 用

atof() 将字符串转换为双精度浮点型值
atoi() 将字符串转换为整型值
atol() 将字符串转换为长整型值
strtod() 将字符串转换为双精度浮点型值，并报告不能被转换的所有剩余数字
strtol() 将字符串转换为长整值，并报告不能被转换的所有剩余数字
strtoul() 将字符串转换为无符号长整型值，并报告不能被转换的所有剩余数字

/* strtod example */
#include       /* printf, NULL */
#include      /* strtod */

int main ()
{
  char szOrbits[] = "365.24 29.53";
  char* pEnd;
  double d1, d2;
  d1 = strtod (szOrbits, &pEnd);
  d2 = strtod (pEnd, NULL);
  printf ("The moon completes %.2f orbits per Earth year.\n", d1/d2);
  return 0;
}

/* strtol example */
#include       /* printf */
#include      /* strtol */

int main ()
{
  char szNumbers[] = "2001 60c0c0 -1101110100110100100000 0x6fffff";
  char * pEnd;
  long int li1, li2, li3, li4;
  li1 = strtol (szNumbers,&pEnd,10);
  li2 = strtol (pEnd,&pEnd,16);
  li3 = strtol (pEnd,&pEnd,2);
  li4 = strtol (pEnd,NULL,0);
  printf ("The decimal equivalents are: %ld, %ld, %ld and %ld.\n", li1, li2, li3, li4);
  return 0;
}

/* strtoul example */
#include       /* printf, NULL */
#include      /* strtoul */

int main ()
{
  char buffer [256];
  unsigned long ul;
  printf ("Enter an unsigned number: ");
  fgets (buffer, 256, stdin);
  ul = strtoul (buffer, NULL, 0);
  printf ("Value entered: %lu. Its double: %lu\n",ul,ul*2);
  return 0;
}