Size_t and ssize_t

Ssize_t and size_t

Track the Linux source code to get the following macros:

 

# Ifndef _ size_t

# DEFINE _ size_t

Typedef _ kernel_size_t size_t;

# Endif

 

# Ifndef _ ssize_t

# DEFINE _ ssize_t

Typedef _ kernel_ssize_t ssize_t;

# Endif

 

Different platforms have different definitions:

/* 64-bit */

Typedef unsigned long _ kernel_size_t;

Typedef long _ kernel_ssize_t;

 

/* Linux 32 bit */

Typedef unsigned int _ kernel_size_t;

Typedef int _ kernel_ssize_t;

This is the actual definition of two types, literally:

Ssize_t = signed size_t

 

Usage location:

Size_t is generally used for the length of non-negative values such as the buffer size;

For Image

Ssize_t (* read) (struct file *, char _ User *, size_t, loff_t *);

Ssize_t (* write) (struct file *, const char _ User *, size_t, loff_t *);

Ssize_t (* aio_read) (struct kiocb *, const struct iovec *, unsigned long, loff_t );

Ssize_t (* aio_write) (struct kiocb *, const struct iovec *, unsigned long, loff_t );

If the <0 function is returned for failure, ssize_t is used;

 

Ssize_t (* read) (struct file *, char _ User *, size_t, loff_t *);

Another similar type: loff_t

Definition:

# If defined (_ gnuc __)

Typedef _ kernel_loff_t loff_t;

# Endif

Is a long type.

# Ifdef _ gnuc __

Typedef long _ kernel_loff_t;

# Endif

More: http://blog.csdn.net/lalor/article/details/7426184

Size_t and ssize_t