如何在不指定大小的情况下将无限字符读入char*
变量中?
例如,假设我想要读取一个可能包含多行的员工地址。
如何在不指定大小的情况下将无限字符读入char*
变量中?
例如,假设我想要读取一个可能包含多行的员工地址。
首先你需要“猜测”所需的大小,然后使用malloc
分配一个这么大的缓冲区。如果发现缓冲区太小,可以使用realloc
来将缓冲区调整为更大的尺寸。示例代码:
char *buffer;
size_t num_read;
size_t buffer_size;
buffer_size = 100;
buffer = malloc(buffer_size);
num_read = 0;
while (!finished_reading()) {
char c = getchar();
if (num_read >= buffer_size) {
char *new_buffer;
buffer_size *= 2; // try a buffer that's twice as big as before
new_buffer = realloc(buffer, buffer_size);
if (new_buffer == NULL) {
free(buffer);
/* Abort - out of memory */
}
buffer = new_buffer;
}
buffer[num_read] = c;
num_read++;
}
这只是我随意想到的,可能(读作:很有可能)包含错误,但应该能给您一个好的想法。
x = realloc(x, newsize);
如果realloc失败,你将失去原始指针并且会造成内存泄漏。尽管如此,有一个例外是如果你的分配失败策略是结束进程,那么这样做是可以的。 - R Samuel Klatchkovoid *sav=ptr; if((ptr=realloc(ptr,newsiz))==null) { free(sav); }
- Lawrence Dolrealloc(buffer, num_read)
调用,将分配的缓冲区修剪到所需的确切大小。 - caf/*realloc_for_averaging_value_of_floats_fri14Sept2012_16:30 */
#include <stdio.h>
#include <stdlib.h>
#define TRUE 1
int main(int argc, char ** argv[])
{
float input = 0;
int count=0, n = 0;
float *numbers = NULL;
float *more_numbers;
float sum = 0.0;
while (TRUE)
{
do
{
printf("Enter an floating point value (0 to end): ");
scanf("%f", &input);
count++;
more_numbers = (float*) realloc(numbers, count * sizeof(float));
if ( more_numbers != NULL )
{
numbers = more_numbers;
numbers[count - 1] = input;
}
else
{
free(numbers);
puts("Error (re)allocating memory");
exit(TRUE);
}
} while ( input != 0 );
printf("Numbers entered: ");
while( n < count )
{
printf("%f ", numbers[n]); /* n is always less than count.*/
n++;
}
/*need n++ otherwise loops forever*/
n = 0;
while( n < count )
{
sum += numbers[n]; /*Add numbers together*/
n++;
}
/* Divide sum / count = average.*/
printf("\n Average of floats = %f \n", sum / (count - 1));
}
return 0;
}
/* Success Fri Sept 14 13:29 . That was hard work.*/
/* Always looks simple when working.*/
/* Next step is to use a function to work out the average.*/
/*Anonymous on July 04, 2012*/
/* http://www.careercup.com/question?id=14193663 */
你可以在栈上放置一个1KB缓冲区(或4KB),读取数据直到找到地址的结尾,然后分配正确大小的缓冲区并将数据复制到其中。一旦从函数返回,栈缓冲区就会消失,你只需要调用一次malloc
。
fgets
有一个缓冲区大小的参数。标准C库中肯定有要避免使用的函数(如gets
)。使用长度限制函数和固定大小缓冲区对我来说似乎非常安全。 - tomlogic
getline
。 - dmckee --- ex-moderator kitten