当我将 Scanf 放入它自己的函数中时它不起作用？
When i put Scanf in it own function it doesn't work?
我编写了这段用于乘法矩阵的代码。它可以工作，但是当我尝试将它放入它自己的函数中时，它会停止工作。为什么要这样做？
#include <stdio.h>
#include <stdlib.h>
/* Ask for elements to insert inside matrixes.*/
void AddValues(int row, int col, float **ptr, int matrixNumber) {
printf("\nWrite elements to insert into %d. matrix :\n", matrixNumber);
for (int i = 0; i < row; i++) {
for (int j = 0; j < col; j++) {
printf("\tA[%d][%d] = ", i, j);
scanf("%f", &ptr[i][j]);
}
}
}
void Multiply(int row1, int col1, int col2, float **ptr1, float **ptr2, float **ptr3) {
/* Multiplication. */
for (int i = 0; i < row1; i++) {
for (int j = 0; j < col1; j++) {
ptr3[i][j] = 0;
for (int k = 0; k < col2; k++)
ptr3[i][j] = ptr3[i][j] + ptr1[i][k] * ptr2[k][j];
}
}
}
void WriteOut(int row1, int col2, float **ptr3) {
/* Print final matrix. */
printf("\n\nFinal Matrix :");
for (int i = 0; i < row1; i++) {
printf("\n\t\t\t");
for (int j = 0; j < col2; j++)
printf("%f\t", ptr3[i][j]);
}
}
void HighestSum(int row1, int col2, float **ptr3) {
printf("\n\nrow with highest sum of elements :");
float max = 0;
float sum;
for (int i = 0; i < row1; ++i) {
for (int j = 0; j < col2; ++j){
sum = sum + ptr3[i][j];
if (j == col2 - 1)
printf("\n");
}
if (max == 0)
max = sum;
if (max < sum)
max = sum;
sum = 0;
}
printf("Highest sum of elements in row: %f ", max);
}
int main() {
float **ptr1, **ptr2, **ptr3;
int row1, col1, row2, col2;
int i;
printf("\nWrite numbers of rows for first matrix. : ");
scanf("%d", &row1);
printf("\nWrite numbers of columns for first matrix. : ");
scanf("%d", &col1);
printf("\nWrite numbers of rows for second matrix. : ");
scanf("%d", &row2);
printf("\nWrite numbers of columns for second matrix. : ");
scanf("%d", &col2);
if (col1 != row2) {
printf("\nMatrixes can't be multiplied.");
return (0);
}
if (col1 <= 0 || row1 <= 0 || col2 <= 0 || row2 <= 0) {
printf("\nNumbers have to be positive.");
return (0);
}
/* Allocation. */
ptr1 = (float **)malloc(sizeof(float *) * row1);
ptr2 = (float **)malloc(sizeof(float *) * row2);
ptr3 = (float **)malloc(sizeof(float *) * row1);
for (i = 0; i < row1; i++)
ptr1[i] = (float *)malloc(sizeof(float) * col1);
for (i = 0; i < row2; i++)
ptr2[i] = (float *)malloc(sizeof(float) * col2);
for (i = 0; i < row1; i++)
ptr3[i] = (float *)malloc(sizeof(float) * col2);
AddValues(row1, col1, ptr1, 1);
AddValues(row2, col2, ptr2, 2);
Multiply(row1, col1, col2, ptr1, ptr2, ptr3);
WriteOut(row1, col2, ptr3);
HighestSum(row1, col2, ptr3);
return 0;
}
这样写的程序可以运行。然而，当我把 scanf 放在它自己的函数中时，它不会
void Scanner(int row1, int col1, int row2, int col2) {
printf("\nWrite numbers of rows for first matrix. : ");
scanf("%d", &row1);
printf("\nWrite numbers of columns for first matrix. : ");
scanf("%d", &col1);
printf("\nWrite numbers of rows for second matrix. : ");
scanf("%d", &row2);
printf("\nWrite numbers of columns for second matrix. : ");
scanf("%d", &col2);
if (col1 != row2) {
printf("\nMatrixes can't be multiplied.");
return (0);
}
if (col1 <= 0 || row1 <= 0 || col2 <= 0 || row2 <= 0) {
printf("\nNumbers have to be positive.");
return (0);
}
}
该程序将询问行和列的大小，但随后停止。我怎样才能让它发挥作用？
在函数Scanner中，参数是按值传递的。这意味着函数 Scanner 将获得这些变量自己的副本，并且更改这些副本的值不会更改函数 main.
中原始变量的值
如果你想让函数Scanner能够改变函数main中的原始变量的值，那么你不应该传递原始变量的值，但是你应该而是传递指向函数 main 中原始变量的指针。这样，函数 Scanner 可以使用指针直接写入原始变量。
我建议您将函数 Scanner 更改为以下内容：
void Scanner( int *p_row1, int *p_col1, int *p_row2, int *p_col2 )
{
printf( "Write numbers of rows for first matrix: " );
scanf( "%d", p_row1 );
printf( "Write numbers of columns for first matrix: " );
scanf( "%d", p_col1 );
printf( "Write numbers of rows for second matrix: " );
scanf( "%d", p_row2 );
printf( "Write numbers of columns for second matrix: " );
scanf( "%d", p_col2 );
if( *p_col1 != *p_row2 )
{
printf( "Matrixes can't be multiplied.\n" );
exit( EXIT_FAILURE );
}
if( *p_col1 <= 0 || *p_row1 <= 0 || *p_col2 <= 0 || *p_row2 <= 0 )
{
printf( "Numbers have to be positive.\n" );
exit( EXIT_FAILURE );
}
}
我在变量名中添加的前缀p_只是代表“指针”，但您不必使用该前缀。你可以给他们任何你想要的名字。
您可以像这样从函数 main 调用函数 Scanner：
Scanner( &row1, &col1, &row2, &col2 );
此外，由于您正在处理用户输入，因此最好始终检查 scanf 的 return 值，以确定函数是否成功。否则，如果用户输入的不是数字，转换将失败，但您的程序仍将尝试处理 non-existant 转换后的值。
因此，这样写函数可能会更好：
void Scanner( int *p_row1, int *p_col1, int *p_row2, int *p_col2 )
{
printf( "Write numbers of rows for first matrix: " );
if ( scanf( "%d", p_row1 ) != 1 )
{
printf( "Input error!\n" );
exit( EXIT_FAILURE );
}
printf( "Write numbers of columns for first matrix: " );
if ( scanf( "%d", p_col1 ) != 1 )
{
printf( "Input error!\n" );
exit( EXIT_FAILURE );
}
printf( "Write numbers of rows for second matrix: " );
if ( scanf( "%d", p_row2 ) != 1 )
{
printf( "Input error!\n" );
exit( EXIT_FAILURE );
}
printf( "Write numbers of columns for second matrix: " );
if ( scanf( "%d", p_col2 ) != 1 )
{
printf( "Input error!\n" );
exit( EXIT_FAILURE );
}
if( *p_col1 != *p_row2 )
{
printf( "Matrixes can't be multiplied.\n" );
exit( EXIT_FAILURE );
}
if( *p_col1 <= 0 || *p_row1 <= 0 || *p_col2 <= 0 || *p_row2 <= 0 )
{
printf( "Numbers have to be positive.\n" );
exit( EXIT_FAILURE );
}
}
但是，这个解决方案仍然没有很好地执行输入验证。例如，如果用户输入数字 6abc，那么 scanf 将接受此输入作为数字 6 的有效输入。如果您不想这样做，那么您可能需要使用 中的函数 get_int_from_user。该函数将执行非常严格的输入验证，如果输入不是数字，它将自动重新提示用户输入。
如果您决定使用我的函数 get_int_from_user，那么您可以这样编写函数：
void Scanner( int *p_row1, int *p_col1, int *p_row2, int *p_col2 )
{
*p_row1 = get_int_from_user(
"Write numbers of rows for first matrix: "
);
*p_col1 = get_int_from_user(
"Write numbers of columns for first matrix: "
);
*p_row2 = get_int_from_user(
"Write numbers of rows for second matrix: "
);
*p_col2 = get_int_from_user(
"Write numbers of columns for second matrix: "
);
if( *p_col1 != *p_row2 )
{
printf( "Matrixes can't be multiplied.\n" );
exit( EXIT_FAILURE );
}
if( *p_col1 <= 0 || *p_row1 <= 0 || *p_col2 <= 0 || *p_row2 <= 0 )
{
printf( "Numbers have to be positive.\n" );
exit( EXIT_FAILURE );
}
}
不过，现在当输入的不是数字时，函数 get_int_from_user 会自动重新提示用户，但当输入因其他原因无效时，根本不会重新提示用户。为了解决这个不一致，函数可以这样写：
void Scanner( int *p_row1, int *p_col1, int *p_row2, int *p_col2 )
{
//loop forever until input is valid
for (;;) //infinite loop, equivalent to while(1)
{
*p_row1 = get_int_from_user(
"Write numbers of rows for first matrix: "
);
*p_col1 = get_int_from_user(
"Write numbers of columns for first matrix: "
);
*p_row2 = get_int_from_user(
"Write numbers of rows for second matrix: "
);
*p_col2 = get_int_from_user(
"Write numbers of columns for second matrix: "
);
if( *p_col1 != *p_row2 )
{
printf( "Matrixes can't be multiplied. Try again!\n\n" );
continue;
}
if( *p_col1 <= 0 || *p_row1 <= 0 || *p_col2 <= 0 || *p_row2 <= 0 )
{
printf( "Numbers have to be positive.\n\n" );
continue;
}
//input is valid, so we can break out of the infinite loop
break;
}
}
可以通过在用户输入一个 non-positive 号码后立即重新启动输入来进一步改进此程序，而不是等到用户输入所有 4 个号码。不过，我不想让我的回答太复杂。
这里是最新版本功能的一个小演示程序Scanner:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <limits.h>
#include <errno.h>
void Scanner( int *p_row1, int *p_col1, int *p_row2, int *p_col2 );
int get_int_from_user( const char *prompt );
int main( void )
{
int row1, col1, row2, col2;
Scanner( &row1, &col1, &row2, &col2 );
printf(
"\n"
"The variables in the function main now have the\n"
"following values:\n"
"\n"
"row1: %d\n"
"col1: %d\n"
"row2: %d\n"
"col2: %d\n",
row1, col1, row2, col2
);
}
void Scanner( int *p_row1, int *p_col1, int *p_row2, int *p_col2 )
{
//loop forever until input is valid
for (;;) //infinite loop, equivalent to while(1)
{
*p_row1 = get_int_from_user(
"Write numbers of rows for first matrix: "
);
*p_col1 = get_int_from_user(
"Write numbers of columns for first matrix: "
);
*p_row2 = get_int_from_user(
"Write numbers of rows for second matrix: "
);
*p_col2 = get_int_from_user(
"Write numbers of columns for second matrix: "
);
if( *p_col1 != *p_row2 )
{
printf( "Matrixes can't be multiplied. Try again!\n\n" );
continue;
}
if( *p_col1 <= 0 || *p_row1 <= 0 || *p_col2 <= 0 || *p_row2 <= 0 )
{
printf( "Numbers have to be positive.\n\n" );
continue;
}
//input is valid, so we can break out of the infinite loop
break;
}
}
int get_int_from_user( const char *prompt )
{
for (;;) //loop forever until user enters a valid number
{
char buffer[1024], *p;
long l;
//prompt user for input
fputs( prompt, stdout );
//get one line of input from input stream
if ( fgets( buffer, sizeof buffer, stdin ) == NULL )
{
fprintf( stderr, "unrecoverable error reading from input!\n" );
exit( EXIT_FAILURE );
}
//make sure that entire line was read in (i.e. that
//the buffer was not too small)
if ( strchr( buffer, '\n' ) == NULL && !feof( stdin ) )
{
int c;
printf( "line input was too long!\n" );
//discard remainder of line
do
{
c = getchar();
if ( c == EOF )
{
fprintf( stderr, "unrecoverable error reading from input!\n" );
exit( EXIT_FAILURE );
}
} while ( c != '\n' );
continue;
}
//attempt to convert string to number
errno = 0;
l = strtol( buffer, &p, 10 );
if ( p == buffer )
{
printf( "error converting string to number!\n" );
continue;
}
//make sure that number is representable as an "int"
if ( errno == ERANGE || l < INT_MIN || l > INT_MAX )
{
printf( "number out of range error!\n" );
continue;
}
//make sure that remainder of line contains only whitespace,
//so that input such as "6sdfj23jlj" gets rejected
for ( ; *p != '[=15=]'; p++ )
{
if ( !isspace( (unsigned char)*p ) )
{
printf( "unexpected input encountered!\n" );
//cannot use `continue` here, because that would go to
//the next iteration of the innermost loop, but we
//want to go to the next iteration of the outer loop
goto continue_outer_loop;
}
}
return l;
continue_outer_loop:
continue;
}
}
此程序具有以下行为
Write numbers of rows for first matrix: abc
error converting string to number!
Write numbers of rows for first matrix: 6abc
unexpected input encountered!
Write numbers of rows for first matrix: 6
Write numbers of columns for first matrix: 7
Write numbers of rows for second matrix: 8
Write numbers of columns for second matrix: 9
Matrixes can't be multiplied. Try again!
Write numbers of rows for first matrix: 6
Write numbers of columns for first matrix: 7
Write numbers of rows for second matrix: 7
Write numbers of columns for second matrix: 8
The variables in the function main now have the
following values:
row1: 6
col1: 7
row2: 7
col2: 8
我编写了这段用于乘法矩阵的代码。它可以工作，但是当我尝试将它放入它自己的函数中时，它会停止工作。为什么要这样做？
#include <stdio.h>
#include <stdlib.h>
/* Ask for elements to insert inside matrixes.*/
void AddValues(int row, int col, float **ptr, int matrixNumber) {
printf("\nWrite elements to insert into %d. matrix :\n", matrixNumber);
for (int i = 0; i < row; i++) {
for (int j = 0; j < col; j++) {
printf("\tA[%d][%d] = ", i, j);
scanf("%f", &ptr[i][j]);
}
}
}
void Multiply(int row1, int col1, int col2, float **ptr1, float **ptr2, float **ptr3) {
/* Multiplication. */
for (int i = 0; i < row1; i++) {
for (int j = 0; j < col1; j++) {
ptr3[i][j] = 0;
for (int k = 0; k < col2; k++)
ptr3[i][j] = ptr3[i][j] + ptr1[i][k] * ptr2[k][j];
}
}
}
void WriteOut(int row1, int col2, float **ptr3) {
/* Print final matrix. */
printf("\n\nFinal Matrix :");
for (int i = 0; i < row1; i++) {
printf("\n\t\t\t");
for (int j = 0; j < col2; j++)
printf("%f\t", ptr3[i][j]);
}
}
void HighestSum(int row1, int col2, float **ptr3) {
printf("\n\nrow with highest sum of elements :");
float max = 0;
float sum;
for (int i = 0; i < row1; ++i) {
for (int j = 0; j < col2; ++j){
sum = sum + ptr3[i][j];
if (j == col2 - 1)
printf("\n");
}
if (max == 0)
max = sum;
if (max < sum)
max = sum;
sum = 0;
}
printf("Highest sum of elements in row: %f ", max);
}
int main() {
float **ptr1, **ptr2, **ptr3;
int row1, col1, row2, col2;
int i;
printf("\nWrite numbers of rows for first matrix. : ");
scanf("%d", &row1);
printf("\nWrite numbers of columns for first matrix. : ");
scanf("%d", &col1);
printf("\nWrite numbers of rows for second matrix. : ");
scanf("%d", &row2);
printf("\nWrite numbers of columns for second matrix. : ");
scanf("%d", &col2);
if (col1 != row2) {
printf("\nMatrixes can't be multiplied.");
return (0);
}
if (col1 <= 0 || row1 <= 0 || col2 <= 0 || row2 <= 0) {
printf("\nNumbers have to be positive.");
return (0);
}
/* Allocation. */
ptr1 = (float **)malloc(sizeof(float *) * row1);
ptr2 = (float **)malloc(sizeof(float *) * row2);
ptr3 = (float **)malloc(sizeof(float *) * row1);
for (i = 0; i < row1; i++)
ptr1[i] = (float *)malloc(sizeof(float) * col1);
for (i = 0; i < row2; i++)
ptr2[i] = (float *)malloc(sizeof(float) * col2);
for (i = 0; i < row1; i++)
ptr3[i] = (float *)malloc(sizeof(float) * col2);
AddValues(row1, col1, ptr1, 1);
AddValues(row2, col2, ptr2, 2);
Multiply(row1, col1, col2, ptr1, ptr2, ptr3);
WriteOut(row1, col2, ptr3);
HighestSum(row1, col2, ptr3);
return 0;
}
这样写的程序可以运行。然而，当我把 scanf 放在它自己的函数中时，它不会
void Scanner(int row1, int col1, int row2, int col2) {
printf("\nWrite numbers of rows for first matrix. : ");
scanf("%d", &row1);
printf("\nWrite numbers of columns for first matrix. : ");
scanf("%d", &col1);
printf("\nWrite numbers of rows for second matrix. : ");
scanf("%d", &row2);
printf("\nWrite numbers of columns for second matrix. : ");
scanf("%d", &col2);
if (col1 != row2) {
printf("\nMatrixes can't be multiplied.");
return (0);
}
if (col1 <= 0 || row1 <= 0 || col2 <= 0 || row2 <= 0) {
printf("\nNumbers have to be positive.");
return (0);
}
}
该程序将询问行和列的大小，但随后停止。我怎样才能让它发挥作用？
在函数Scanner中，参数是按值传递的。这意味着函数 Scanner 将获得这些变量自己的副本，并且更改这些副本的值不会更改函数 main.
如果你想让函数Scanner能够改变函数main中的原始变量的值，那么你不应该传递原始变量的值，但是你应该而是传递指向函数 main 中原始变量的指针。这样，函数 Scanner 可以使用指针直接写入原始变量。
我建议您将函数 Scanner 更改为以下内容：
void Scanner( int *p_row1, int *p_col1, int *p_row2, int *p_col2 )
{
printf( "Write numbers of rows for first matrix: " );
scanf( "%d", p_row1 );
printf( "Write numbers of columns for first matrix: " );
scanf( "%d", p_col1 );
printf( "Write numbers of rows for second matrix: " );
scanf( "%d", p_row2 );
printf( "Write numbers of columns for second matrix: " );
scanf( "%d", p_col2 );
if( *p_col1 != *p_row2 )
{
printf( "Matrixes can't be multiplied.\n" );
exit( EXIT_FAILURE );
}
if( *p_col1 <= 0 || *p_row1 <= 0 || *p_col2 <= 0 || *p_row2 <= 0 )
{
printf( "Numbers have to be positive.\n" );
exit( EXIT_FAILURE );
}
}
我在变量名中添加的前缀p_只是代表“指针”，但您不必使用该前缀。你可以给他们任何你想要的名字。
您可以像这样从函数 main 调用函数 Scanner：
Scanner( &row1, &col1, &row2, &col2 );
此外，由于您正在处理用户输入，因此最好始终检查 scanf 的 return 值，以确定函数是否成功。否则，如果用户输入的不是数字，转换将失败，但您的程序仍将尝试处理 non-existant 转换后的值。
因此，这样写函数可能会更好：
void Scanner( int *p_row1, int *p_col1, int *p_row2, int *p_col2 )
{
printf( "Write numbers of rows for first matrix: " );
if ( scanf( "%d", p_row1 ) != 1 )
{
printf( "Input error!\n" );
exit( EXIT_FAILURE );
}
printf( "Write numbers of columns for first matrix: " );
if ( scanf( "%d", p_col1 ) != 1 )
{
printf( "Input error!\n" );
exit( EXIT_FAILURE );
}
printf( "Write numbers of rows for second matrix: " );
if ( scanf( "%d", p_row2 ) != 1 )
{
printf( "Input error!\n" );
exit( EXIT_FAILURE );
}
printf( "Write numbers of columns for second matrix: " );
if ( scanf( "%d", p_col2 ) != 1 )
{
printf( "Input error!\n" );
exit( EXIT_FAILURE );
}
if( *p_col1 != *p_row2 )
{
printf( "Matrixes can't be multiplied.\n" );
exit( EXIT_FAILURE );
}
if( *p_col1 <= 0 || *p_row1 <= 0 || *p_col2 <= 0 || *p_row2 <= 0 )
{
printf( "Numbers have to be positive.\n" );
exit( EXIT_FAILURE );
}
}
但是，这个解决方案仍然没有很好地执行输入验证。例如，如果用户输入数字 6abc，那么 scanf 将接受此输入作为数字 6 的有效输入。如果您不想这样做，那么您可能需要使用 get_int_from_user。该函数将执行非常严格的输入验证，如果输入不是数字，它将自动重新提示用户输入。
如果您决定使用我的函数 get_int_from_user，那么您可以这样编写函数：
void Scanner( int *p_row1, int *p_col1, int *p_row2, int *p_col2 )
{
*p_row1 = get_int_from_user(
"Write numbers of rows for first matrix: "
);
*p_col1 = get_int_from_user(
"Write numbers of columns for first matrix: "
);
*p_row2 = get_int_from_user(
"Write numbers of rows for second matrix: "
);
*p_col2 = get_int_from_user(
"Write numbers of columns for second matrix: "
);
if( *p_col1 != *p_row2 )
{
printf( "Matrixes can't be multiplied.\n" );
exit( EXIT_FAILURE );
}
if( *p_col1 <= 0 || *p_row1 <= 0 || *p_col2 <= 0 || *p_row2 <= 0 )
{
printf( "Numbers have to be positive.\n" );
exit( EXIT_FAILURE );
}
}
不过，现在当输入的不是数字时，函数 get_int_from_user 会自动重新提示用户，但当输入因其他原因无效时，根本不会重新提示用户。为了解决这个不一致，函数可以这样写：
void Scanner( int *p_row1, int *p_col1, int *p_row2, int *p_col2 )
{
//loop forever until input is valid
for (;;) //infinite loop, equivalent to while(1)
{
*p_row1 = get_int_from_user(
"Write numbers of rows for first matrix: "
);
*p_col1 = get_int_from_user(
"Write numbers of columns for first matrix: "
);
*p_row2 = get_int_from_user(
"Write numbers of rows for second matrix: "
);
*p_col2 = get_int_from_user(
"Write numbers of columns for second matrix: "
);
if( *p_col1 != *p_row2 )
{
printf( "Matrixes can't be multiplied. Try again!\n\n" );
continue;
}
if( *p_col1 <= 0 || *p_row1 <= 0 || *p_col2 <= 0 || *p_row2 <= 0 )
{
printf( "Numbers have to be positive.\n\n" );
continue;
}
//input is valid, so we can break out of the infinite loop
break;
}
}
可以通过在用户输入一个 non-positive 号码后立即重新启动输入来进一步改进此程序，而不是等到用户输入所有 4 个号码。不过，我不想让我的回答太复杂。
这里是最新版本功能的一个小演示程序Scanner:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <limits.h>
#include <errno.h>
void Scanner( int *p_row1, int *p_col1, int *p_row2, int *p_col2 );
int get_int_from_user( const char *prompt );
int main( void )
{
int row1, col1, row2, col2;
Scanner( &row1, &col1, &row2, &col2 );
printf(
"\n"
"The variables in the function main now have the\n"
"following values:\n"
"\n"
"row1: %d\n"
"col1: %d\n"
"row2: %d\n"
"col2: %d\n",
row1, col1, row2, col2
);
}
void Scanner( int *p_row1, int *p_col1, int *p_row2, int *p_col2 )
{
//loop forever until input is valid
for (;;) //infinite loop, equivalent to while(1)
{
*p_row1 = get_int_from_user(
"Write numbers of rows for first matrix: "
);
*p_col1 = get_int_from_user(
"Write numbers of columns for first matrix: "
);
*p_row2 = get_int_from_user(
"Write numbers of rows for second matrix: "
);
*p_col2 = get_int_from_user(
"Write numbers of columns for second matrix: "
);
if( *p_col1 != *p_row2 )
{
printf( "Matrixes can't be multiplied. Try again!\n\n" );
continue;
}
if( *p_col1 <= 0 || *p_row1 <= 0 || *p_col2 <= 0 || *p_row2 <= 0 )
{
printf( "Numbers have to be positive.\n\n" );
continue;
}
//input is valid, so we can break out of the infinite loop
break;
}
}
int get_int_from_user( const char *prompt )
{
for (;;) //loop forever until user enters a valid number
{
char buffer[1024], *p;
long l;
//prompt user for input
fputs( prompt, stdout );
//get one line of input from input stream
if ( fgets( buffer, sizeof buffer, stdin ) == NULL )
{
fprintf( stderr, "unrecoverable error reading from input!\n" );
exit( EXIT_FAILURE );
}
//make sure that entire line was read in (i.e. that
//the buffer was not too small)
if ( strchr( buffer, '\n' ) == NULL && !feof( stdin ) )
{
int c;
printf( "line input was too long!\n" );
//discard remainder of line
do
{
c = getchar();
if ( c == EOF )
{
fprintf( stderr, "unrecoverable error reading from input!\n" );
exit( EXIT_FAILURE );
}
} while ( c != '\n' );
continue;
}
//attempt to convert string to number
errno = 0;
l = strtol( buffer, &p, 10 );
if ( p == buffer )
{
printf( "error converting string to number!\n" );
continue;
}
//make sure that number is representable as an "int"
if ( errno == ERANGE || l < INT_MIN || l > INT_MAX )
{
printf( "number out of range error!\n" );
continue;
}
//make sure that remainder of line contains only whitespace,
//so that input such as "6sdfj23jlj" gets rejected
for ( ; *p != '[=15=]'; p++ )
{
if ( !isspace( (unsigned char)*p ) )
{
printf( "unexpected input encountered!\n" );
//cannot use `continue` here, because that would go to
//the next iteration of the innermost loop, but we
//want to go to the next iteration of the outer loop
goto continue_outer_loop;
}
}
return l;
continue_outer_loop:
continue;
}
}
此程序具有以下行为
Write numbers of rows for first matrix: abc
error converting string to number!
Write numbers of rows for first matrix: 6abc
unexpected input encountered!
Write numbers of rows for first matrix: 6
Write numbers of columns for first matrix: 7
Write numbers of rows for second matrix: 8
Write numbers of columns for second matrix: 9
Matrixes can't be multiplied. Try again!
Write numbers of rows for first matrix: 6
Write numbers of columns for first matrix: 7
Write numbers of rows for second matrix: 7
Write numbers of columns for second matrix: 8
The variables in the function main now have the
following values:
row1: 6
col1: 7
row2: 7
col2: 8